Changes: Menstrual cycle

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The menstrual cycle is a recurring cycle of physiological changes that occurs in the females of several mammals, including human beings and other apes.^[1] Humans are the only species that has a menstrual cycle with concealed ovulation. Other placental mammals experience an estrous, where imminent ovulation is signaled to the males of the species.

The menstrual cycle is under the control of the hormone system and is necessary for reproduction. This article concentrates on the menstrual cycle as it occurs in human beings.

Overview

A woman's first menstruation is termed menarche, and is one of the later stages of puberty in girls. The average age of menarche in humans is 12 years, but is normal anywhere between ages 8 and 16. Factors such as heredity, diet and overall health can accelerate or delay menarche.^[2] The cessation of menstrual cycles at the end of a woman's reproductive life is termed menopause. The average age of menopause in women is 51 years, with anywhere between 40 and 58 being common. Menopause before age 35 is considered premature. The age of menopause is largely a result of genetics; however, illness, certain surgeries, or medical treatments may cause menopause to occur earlier.^[3]

The length of a woman's menstrual cycle will typically vary, with some shorter cycles and some longer cycles. A woman who experiences variations of less than eight days between her longest cycles and shortest cycles is considered to have regular menstrual cycles. It is unusual for a woman to experience cycle length variations of less than four days. Length variation between eight and 20 days is considered moderately irregular. Variation of 21 days or more between a woman's shortest and longest cycle lengths is considered very irregular (see cycle abnormalities).^[4]

Menstrual cycles are counted from the first day of menstrual bleeding, because the onset of menstruation corresponds closely with the hormonal cycle. The menstrual cycle may be divided into several phases, and the length of each phase varies from woman to woman and cycle to cycle. Average values are shown below:

Name of phase	Days
menstrual phase	1–4
follicular phase (also known as proliferative phase)	5–13
ovulation (not a phase, but an event dividing phases)	14
luteal phase (also known as secretory phase)	15–26
ischemic phase (some sources group this with secretory phase)	27–28

During the follicular phase the lining of the uterus thickens, stimulated by gradually increasing amounts of estrogen. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two follicles become dominant (non-dominant follicles atrophy and die). The dominant follicle releases an ovum or egg in an event called ovulation. (An egg that is fertilized by a spermatozoon will become a zygote, taking one to two weeks to travel down the fallopian tubes to the uterus. If the egg is not fertilized within about a day of ovulation, it will die and be absorbed by the woman's body^[5].) After ovulation the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will die, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining in a process termed menstruation.

Phases of the menstrual cycle

Menstruation

Main article: Menstruation

Menstruation is also called menstrual bleeding, menses, a period or catamenia. This bleeding normally serves as a sign that a woman has not become pregnant. (However, this cannot be taken as certainty, as sometimes there is some bleeding in early pregnancy.) During the reproductive years, failure to menstruate may provide the first indication to a woman that she may have become pregnant. A woman might say that her "period is late" when an expected menstruation has not started and she might have become pregnant.

Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).^[6] The average blood loss during menstruation is 35 millilitres with 10–80 mL considered normal;^[7] many women also notice shedding of the endometrium lining that appears as tissue mixed with the blood. An enzyme called plasmin — contained in the endometrium — tends to inhibit the blood from clotting. Because of this blood loss, women have higher dietary requirements for iron than do males to prevent iron deficiency. Many women experience uterine cramps during this time (severe cramps or other symptoms are called dysmenorrhea). A vast industry of sanitary products has grown to help women during their menstruation.

Follicular phase

Main article: Follicular phase

Through the influence of a rise in follicle stimulating hormone (FSH), five to seven tertiary-stage ovarian follicles are recruited for entry into the next menstrual cycle. These follicles, that have been growing for the better part of a year in a process known as folliculogenesis, compete with each other for dominance. Under the influence of several hormones, all but one of these follicles will undergo atresia, while one (or occasionally two) dominant follicles will continue to maturity. As they mature, the follicles secrete increasing amounts of estradiol, an oestrogen.

The oestrogens that follicles secrete, initiate the formation of a new layer of endometrium in the uterus, histologically identified as the proliferative endometrium. The estrogen also stimulates crypts in the cervix to produce fertile cervical mucus, which may be noticed by women practicing fertility awareness.

Ovulation

Main article: Ovulation

When the egg has matured, it secretes enough estradiol to trigger the acute release of luteinizing hormone (LH). In the average cycle this LH surge starts around cycle day 12 and may last 48 hours. The release of LH matures the egg and weakens the wall of the follicle in the ovary. This process leads to ovulation: the release of the now mature ovum, the largest cell of the body (with a diameter of about 0.5 mm). Which of the two ovaries — left or right — ovulates appears essentially random; no known left/right co-ordination exists. The Fallopian tube needs to capture the egg and provide the site for fertilization. In some women, ovulation features a characteristic pain called mittelschmerz (German term meaning 'middle pain') which may last a few hours. The sudden change in hormones at the time of ovulation also causes light mid-cycle bleeding for some women. An unfertilized egg will eventually disintegrate or dissolve in the uterus.

Luteal phase

Main article: Luteal phase

The corpus luteum is the solid body formed in the ovaries after the egg has been released into the fallopian tube which continues to grow and divide for a while. After ovulation, the residual follicle transforms into the corpus luteum under the support of the pituitary hormones. This corpus luteum will produce progesterone in addition to estrogens for approximately the next 2 weeks. Progesterone plays a vital role in converting the proliferative endometrium into a secretory lining receptive for implantation and supportive of the early pregnancy. It raises the body temperature by one-half to one degree Fahrenheit (one-quarter to one-half degree Celsius), thus women who record their temperature on a daily basis will notice that they have entered the luteal phase. If fertilization of an egg has occurred, it will travel as an early blastocyst through the fallopian tube to the uterine cavity and implant itself 6 to 12 days after ovulation. Shortly after implantation, the growing embryo will signal its existence to the maternal system. One very early signal consists of human chorionic gonadotropin (hCG), a hormone that pregnancy tests can measure. This signal has an important role in maintaining the corpus luteum and enabling it to continue to produce progesterone. In the absence of a pregnancy and without hCG, the corpus luteum demises and inhibin and progesterone levels fall. This will set the stage for the next cycle. Progesterone withdrawal leads to menstrual shedding (progesterone withdrawal bleeding), and falling inhibin levels allow FSH levels to rise to raise a new crop of follicles.

The fertile window

The length of the follicular phase — and consequently the length of the menstrual cycle — may vary widely. The luteal phase, however, almost always takes the same number of days for each woman: Some women have a luteal phase of 10 days, others 16 days, while the average is 14 days. Sperm survive inside a woman for 3 days on average, with survival time up to five days considered normal. A pregnancy resulting from sperm life of eight days has been documented.^[8]^[9]^[10] The most fertile period (the time with the highest likelihood of pregnancy resulting from sexual intercourse) covers the time from some 5 days before ovulation until 1–2 days after ovulation. In an average 28 day cycle with a 14-day luteal phase, this corresponds to the second and the beginning of the third week of the cycle. Fertility awareness methods of birth control attempt to determine the precise time of ovulation in order to find the relatively fertile and the relatively infertile days in the cycle.

People who have heard about the menstrual cycle and ovulation often mistakenly assume, for contraceptive purposes, that menstrual cycles regularly take 28 days, and that ovulation always occurs 14 days after beginning of the menses. This assumption may lead to unintended pregnancies. Note too that not every bleeding event counts as a menstruation, and this can mislead people in their calculation of the fertile window.

If a woman wants to conceive, the most fertile time occurs between 19 and 10 days prior to the expected menses. Many women use ovulation detection kits that detect the presence of the LH surge in the urine to indicate the most fertile time. Other ovulation detection systems rely on observation of one or more of the three primary fertility signs (basal body temperature, cervical fluid, and cervical position).

Among women living closely together, the onsets of menstruation may tend to synchronise somewhat. This McClintock effect was first described in 1971, and possibly explained by the action of pheromones in 1998.^[11] However, subsequent research has called this conclusion into question.^[12]

Hormonal control

Extreme intricacies regulate the menstrual cycle. For many years, researchers have argued over which regulatory system has ultimate control: the hypothalamus, the pituitary, or the ovary with its growing follicle; but all three systems have to interact. In any scenario, the growing follicle has a critical role: it matures the lining, provides the appropriate feedback to the hypothalamus and pituitary, and modifies the mucus changes at the cervix.

Gonadal

Two sex hormones play a role in the control of the menstrual cycle: estradiol and progesterone:

Estrogen peaks twice, during follicular growth and during the luteal phase.
Progesterone remains virtually absent prior to ovulation, but becomes critical in the luteal phase and during pregnancy. Many tests for ovulation check for the presence of progesterone.

After ovulation the corpus luteum — which develops from the burst follicle and remains in the ovary — secretes both estradiol and progesterone. Only if pregnancy occurs do hormones appear in order to suspend the menstrual cycle, while production of estradiol and progesterone continues. Abnormal hormonal regulation leads to disturbance in the menstrual cycle.

Hypothalamus and pituitary

These sex hormones come under the influence of the pituitary gland, and both FSH and LH play necessary roles:

FSH stimulates immature follicles in the ovaries to grow.
LH triggers ovulation.

The gonadotropin-releasing hormone of the hypothalamus controls the pituitary, yet both the pituitary and the hypothalamus receive feedback from the follicle.

Cyclic effects upon nervous system

Some women with neurological conditions experience increased activity of their conditions at about the same time every month. 80 percent of women with epilepsy have more seizures than usual in the phase of their cycle when progesterone declines and estrogen increases.

Mice have been used as an experimental system to investigate possible mechanisms by which levels of sex steroid hormones might regulate nervous system function. During the part of the mouse oestrous cycle when progesterone is highest, the level of nerve-cell GABA receptor subtype delta was high. Since these GABA receptors are inhibitory, nerve cells with more delta receptors are less likely to fire than cells with lower numbers of delta receptors. During the part of the mouse estrous cycle when estrogen levels are higher than progesterone levels, the number of delta receptors decrease, increasing nerve cell activity, in turn increasing anxiety and seizure susceptibility.^[13]

Hidden ovulation

Main article: Concealed ovulation

Unlike almost all other species, the external physical changes of a human female near ovulation are very subtle. A woman may sense her own ovulation while it may remain indiscernible to others; this is considered to have sociobiological significance. In contrast, other species often signal receptivity through heat, swellings, and/or changes in color in the genital area. Humans are the only mammal to have hidden ovulation, although some argue that the extended estrus period of the bonobo (reproductive-age females are in heat for 75% of their menstrual cycle)^[14] has a similar effect to the lack of a "heat" in human females.^[15]

The ovary as an egg-bank

Evidence suggests that eggs are formed from germ cells early in fetal life. The number is reduced to an estimated 400,000 to 450,000 immature ova residing in each ovary at puberty. The menstrual cycle, as a biologic event, allows for ovulation of one egg typically each month. Thus over her reproductive lifetime a woman will ovulate approximately 400 to 450 times. All the other eggs dissolve by a process called atresia. As a woman's total egg supply is formed in fetal life,^[16] to be ovulated decades later, it has been suggested that this long lifetime may make the chromatin of eggs more vulnerable to division problems, breakage, and mutation than the chromatin of sperm, which are produced continuously during a man's reproductive life.

Cycle abnormalities

Main article: Menstrual disorder

Anovulation

Apparently normal menstrual bleeding can occur without ovulation preceding it (anovulatory cycle - "an-" meaning "absence of" +ovulation). In some women, follicular development may start but not be completed; nevertheless, estrogens will form and will stimulate the uterine lining. Anovulatory bleeding resulting from a very thick endometrium caused by prolonged, continued high estrogen levels is called estrogen breakthrough bleeding. Anovulatory bleeding triggered by a sudden drop in estrogen levels is called estrogen withdrawal bleeding.^[17]

Anovulatory bleeding may occur on a regular basis, but more commonly happens with irregular frequency. Anovulatory bleeding commonly occurs prior to menopause (premenopause) or in women with polycystic ovary syndrome.

Infrequent or irregular ovulation is called oligoovulation.

Flow

Sudden heavy flows or amounts in excess of 80 mL (hypermenorrhea or menorrhagia) are not normal.

Bleeding very little (less than 10mL) is called hypomenorrhea.

Prolonged bleeding (metrorrhagia, also meno-metrorrhagia) no longer shows a clear interval pattern. Dysfunctional uterine bleeding refers to hormonally caused bleeding abnormalities, typically anovulation.

All bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant patients may bleed, a pregnancy test forms part of the evaluation of abnormal bleeding.

Cycle length

The medical term for cycles with intervals of 21 days or fewer is polymenorrhea and, on the other hand, the term for cycles with intervals exceeding 35 days is oligomenorrhea (or amenorrhea if intervals exceed 180 days).

Amenorrhea refers to a prolonged absence of menses during the reproductive years of a woman. For example, women with very low body fat, such as athletes, may cease to menstruate. Amenorrhea also occurs during pregancy.

Early menarche

The condition precocious puberty has caused menstruation to occur in girls as young as eight months old.^[18]

Contraception and menstruation

Hormonal options

Main article: Hormonal contraception

Estrogens and progesterone-like hormones make up the main active ingredients of hormonal birth control methods such as the the pill. Typically they cause regular monthly bleeding that roughly mimics a menstrual cycle in appearance, but suppresses ovulation. With most pills, a woman takes hormone pills for 21 days, followed by 7 days of non-functional placebo pills or no pills at all, then the cycle starts again. During the 7 placebo days, a withdrawal bleeding occurs; this differs from ordinary menstruation, and skipping the placebos and continuing with the next batch of hormone pills may suppress it. (There are two main versions of the pill: monophasic and triphasic. With triphasic pills, skipping placebos and continuing with the next month's dose can make a woman more likely to experience spotting or breakthrough bleeding.) In 2003, the U.S. Food and Drug Administration (FDA) approved low-dose monophasic birth control pills that induce withdrawal bleeding every 3 months. Yet another version of the pill is the Loestrin Fe, which has only a four-day placebo "week" (the placebos are actually iron supplements intended to replenish iron lost by bleeding); the other three placebos are replaced with active hormone pills. This system is intended to help shorten periods. Mircette contains several days of estrogen-only pills in addition to the usual combination estrogen/progestin pills, in the case of women who may have problems with low estrogen during the placebo days with other pills.

Other types of hormonal birth control which affect menstruation include the vaginal Nuvaring and the transdermal patch (like the standard pill pack, it is used for three weeks, followed by a one-week break for bleeding) and the injection (which can eliminate bleeding for three months at a time).

Effects on menstruation

All such methods are designed to regulate monthly bleeding. Because of this, they are often chosen by females who wish to regulate the frequency and length of their period, often for basic convenience and especially when such factors are irregular and problematic on their own. Hormonal contraception has also been shown to improve menstrual factors such as cramping, heavy bleeding, and other bothersome physical and emotional issues related to periods.

Control and flexibility

Hormonal methods which are controlled by the user day-to-day, including pills, the ring, and the patch, need not always be used according to the standard cycle/calendar. Their use can be rescheduled and altered in various ways to postpone or skip periods when desired for reasons of convenience (e.g., traveling or scheduled gynecological exams), personal enjoyment (such as expected sexual encounters or events like a wedding or dance), or health (including very painful periods or sensitivity to hormone fluctuations). Similarly, abrupt cessation of use can induce a breakthrough period mid-cycle.

Other contraceptive methods

Most IUDs are not designed to affect menstruation or breakthrough bleeding, but may exacerbate cramps or the heaviness of the flow due to their placement within the uterus. The Mirena IUD releases a small continuous dosage of a progesterone-like hormone, which can sometimes cause menstruation to cease. Tubal sterilization alone will not affect menstruation, though the ablation option often performed at the same time will cause menstruation to cease. Hysterectomy will, of course, completely stop menstruation as it entails the removal of the uterus (and sometimes the ovaries, fallopian tubes, and cervix). Fertility awareness methods do not affect the period in and of themselves, but involve careful observation of various kinds, of which the timing of the period is an essential factor.

Menstruation and the moon

See also: Culture and menstruation Traditional sources agree that the menstrual cycle is linked to the cycle of the moon. These sources generally indicate that women menstruate at the time of the new moon, and ovulate at the full moon. Although scientific evidence for this has been weak, the problem may be that most women today live in urban environments where the moon is no longer a significant contributor to nocturnal light. The fact that women who work on night shifts, where they are exposed to strong light at night, often experience menstrual irregularities, is just one example of how rhythms of light and darkness do influence hormonal physiology, including the menstrual cycle.^[19]

The very word menstruation is etymologically related to moon. The terms "menstruation" and "menses" come from the Latin mensis (month), which in turn relates to the Greek mene (moon) and to the roots of the English words month and moon — reflecting the fact that the moon also takes close to 28 days to revolve around the Earth (actually 27.32 days). The synodical lunar month, the period between two new moons (or full moons), is 29.53 days long.

A 1975 book by Louise Lacey documented the experience of herself and 27 of her friends, who found that when they removed all artificial nightlighting their menstrual cycles began to occur in rhythm with the lunar cycle. She dubbed the technique Lunaception.^[20] Later studies in both humans^[21] and animals^[22] have found that artificial light at night does influence the menstrual cycle in humans and the estrus cycle in mice (cycles are more regular in the absence of artificial light at night), though none have duplicated the synchronization of women's menstrual cycles with the lunar cycle. One author has suggested that sensitivity of women's cycles to nightlighting is caused by nutritional deficiencies of certain vitamins and minerals.^[23]

Some have suggested that the fact that other animals' menstrual cycles appear to be greatly different from lunar cycles is evidence that the average length of humans' cycle is most likely a coincidence.^[24]^[25]

Menstrual cycles in other mammals

Females of most species advertise ovulation to males with visual cues and behavioral cues, pheromones, or both (humans are a notable exception). This period of advertised fertility is known as estrous or heat. However, in animals with menstrual cycles, females can be sexually active at any time in their cycle, even when they are not in heat. Great apes' cycles vary in length from an average of 29 days in orangutans to an average of 37 days in chimpanzees.

By contrast, in species that have estrous cycles rather than menstrual cycles, females are only receptive to copulation while they are in heat (dolphins are a notable exception). The other significant difference is that in an estrous cycle, if no fertilization takes place, the uterus reabsorbs the endometrium: no menstrual bleeding occurs. Some animals, such as domestic cats and dogs, experience small amounts of bleeding while in heat. This phase of the estrous cycle corresponds most closely to the follicular phase of the menstrual cycle and should not be confused with menstruation.

References

Gangestad SW, Simpson JA, Cousins AJ, Garver-Apgar CE, Christensen PN (2004). Women's preferences for male behavioral displays change across the menstrual cycle. Psychol Sci 15 (3): 203-7. PMID 15016293.

Notes

↑ "ape". Encyclopædia Britannica Britannica Concise Encyclopedia. (2007). Retrieved on 2007-08-03.
↑ "At what age does a girl get her first period?," from Menstruation and the Menstrual Cycle, National Women's Health Information Center (accessed June 11, 2005)
↑ Shuman, Tracy Your Guide to Menopause. WebMD. URL accessed on 2006-12-16.
↑ Kippley, John; Sheila Kippley (1996). The Art of Natural Family Planning, 4th Edition, p. 92, Cincinnati, OH: The Couple to Couple League. ISBN 0-926412-13-2.
↑ http://www.americanpregnancy.org/gettingpregnant/understandingovulation.html
↑ >The National Women's Health Information Center (November 2002). What is a typical menstrual period like?. U.S. Department of Health and Human Services. URL accessed on 2005-06-11.
↑ David L Healy (2004-11-24). Menorrhagia Heavy Periods - Current Issues. Monash University.
↑ Ball M (1976). A prospective field trial of the "ovulation method" of avoiding conception. Eur J Obstet Gynecol Reprod Biol 6 (2): 63-6. PMID 985763.
↑ Dr Evelyn Billings & Ann Westmore (2005). Trials of The Billings Ovulation Method. URL accessed on 2005-11-03.
↑ Sinha G, Sinha A (1993). A field trial of Billings' ovulation method for spacing and limitation of birth. J Indian Med Assoc 91 (10): 255-6. PMID 8308307.
↑ Stern K, McClintock MK (1998). Regulation of ovulation by human pheromones. Nature 392 (6672): 177-9. PMID 9515961.
↑ Adams, Cecil Does menstrual synchrony really exist?. The Straight Dope. The Chicao Reader. URL accessed on 2007-01-10.
↑ Maguire, J.L. . . . and I. Mody. (2005). Ovarian cycle-linked changes in GABA_A receptors mediating tonic inhibition alter seizure susceptibility and anxiety. Nature Neuroscience 8 (June): 797–804.
↑ Lanting, Frans; Waal, F. B. M. de (1997). Bonobo: the forgotten ape, p.107, Berkeley: University of California Press. URL accessed 2007-09-05.
↑ Stanford, Craig B. (March-April 2000). The Brutal Ape vs. the Sexy Ape? The Make-Love-Not-War Ape. American Scientist 88 (2): 110.
↑ Krock, Lexi Fertility Throughout Life. 18 Ways to Make a Baby. NOVA Online. URL accessed on 2006-12-24. Haines, Cynthiac Your Guide to the Female Reproductive System. The Cleveland Clinic Women's Health Center. WebMD. URL accessed on 2006-12-24.
↑ Weschler, Toni (2002). Taking Charge of Your Fertility, Revised Edition, p.107, New York: HarperCollins. ISBN 0-06-093764-5.
↑ Mikkelson, Barbara, David P. Mikkelson Youngest Mother. Snopes.com. URL accessed on 2006-07-02.
↑ Cohen S. "Melatonin, menstruation and the moon" Townsend Letter for Doctors and Patients, Feb-March, 2005.[1]
↑ Lacey, Louise. Lunaception: A Feminine Odyssey into Fertility and Contraception. New York: Coward, McCann & Geoghegan, 1975.
↑ Singer, Katie. "[http://www.westonaprice.org/women/fertility.html Fertility Awareness, Food, and Night-Lighting]". Wise Traditions in Food, Farming and the Healing Arts, Spring 2004. See section on Night-Lighting.
↑ Harder, Ben. Bright nights kindle cancers in mice. Science News, Week of Aug. 28, 2004; Vol. 166, No. 9 , p. 141.
↑ Shannon, Marilyn. Fertility, Cycles, and Nutrition. Cincinnati, Ohio: The Couple to Couple League International, 2001. pp. 71–72.
↑ As cited by Adams, Cecil, "What's the link between the moon and menstruation?" (accessed 6 June 2006): Abell, George O.; Barry Singer (1983). Science and the Paranormal: Probing the Existence of the Supernatural, Scribner Book Company. ISBN 0-684-17820-6.
↑ Cutler WB. Lunar and menstrual phase locking. Am J Obstet Gynecol. 1980 Aug 1;137(7):834-9. PMID: 7405975.
Friedmann E. Menstrual and lunar cycles. Am J Obstet Gynecol. 1981 Jun 1;140(3):350. PMID: 7246643
Law SP. The regulation of menstrual cycle and its relationship to the moon. Acta Obstet Gynecol Scand. 1986;65(1):45-8. PMID: 3716780
Zimecki M. The lunar cycle: effects on human and animal behavior and physiology. Postepy Hig Med Dosw (Online). 2006;60:1–7. Review. PMID: 16407788

External links

This page uses Creative Commons Licensed content from Wikipedia (view authors).

[1] "ape". Encyclopædia Britannica Britannica Concise Encyclopedia. (2007). Retrieved on 2007-08-03.

[age-2] "At what age does a girl get her first period?," from Menstruation and the Menstrual Cycle, National Women's Health Information Center (accessed June 11, 2005)

[3] Shuman, Tracy Your Guide to Menopause. WebMD. URL accessed on 2006-12-16.

[kippley-4] Kippley, John; Sheila Kippley (1996). The Art of Natural Family Planning, 4th Edition, p. 92, Cincinnati, OH: The Couple to Couple League. ISBN 0-926412-13-2.

[5] ttp://www.americanpregnancy.org/gettingpregnant/understandingovulation.html

[US-typical-6] >The National Women's Health Information Center (November 2002). What is a typical menstrual period like?. U.S. Department of Health and Human Services. URL accessed on 2005-06-11.

[7] David L Healy (2004-11-24). Menorrhagia Heavy Periods - Current Issues. Monash University.

[spermlife-8] Ball M (1976). A prospective field trial of the "ovulation method" of avoiding conception. Eur J Obstet Gynecol Reprod Biol 6 (2): 63-6. PMID 985763.

[Billings-9] Dr Evelyn Billings & Ann Westmore (2005). Trials of The Billings Ovulation Method. URL accessed on 2005-11-03.

[JIndianMedAssoc1993-Billings-10] Sinha G, Sinha A (1993). A field trial of Billings' ovulation method for spacing and limitation of birth. J Indian Med Assoc 91 (10): 255-6. PMID 8308307.

[Mclintock-11] Stern K, McClintock MK (1998). Regulation of ovulation by human pheromones. Nature 392 (6672): 177-9. PMID 9515961.

[12] Adams, Cecil Does menstrual synchrony really exist?. The Straight Dope. The Chicao Reader. URL accessed on 2007-01-10.

[Maguire-13] Maguire, J.L. . . . and I. Mody. (2005). Ovarian cycle-linked changes in GABA_A receptors mediating tonic inhibition alter seizure susceptibility and anxiety. Nature Neuroscience 8 (June): 797–804.

[14] Lanting, Frans; Waal, F. B. M. de (1997). Bonobo: the forgotten ape, p.107, Berkeley: University of California Press. URL accessed 2007-09-05.

[15] Stanford, Craig B. (March-April 2000). The Brutal Ape vs. the Sexy Ape? The Make-Love-Not-War Ape. American Scientist 88 (2): 110.

[16] Krock, Lexi Fertility Throughout Life. 18 Ways to Make a Baby. NOVA Online. URL accessed on 2006-12-24. Haines, Cynthiac Your Guide to the Female Reproductive System. The Cleveland Clinic Women's Health Center. WebMD. URL accessed on 2006-12-24.

[tcoyf-17] Weschler, Toni (2002). Taking Charge of Your Fertility, Revised Edition, p.107, New York: HarperCollins. ISBN 0-06-093764-5.

[18] Mikkelson, Barbara, David P. Mikkelson Youngest Mother. Snopes.com. URL accessed on 2006-07-02.

[19] Cohen S. "Melatonin, menstruation and the moon" Townsend Letter for Doctors and Patients, Feb-March, 2005.[1]

[20] Lacey, Louise. Lunaception: A Feminine Odyssey into Fertility and Contraception. New York: Coward, McCann & Geoghegan, 1975.

[21] Singer, Katie. "[http://www.westonaprice.org/women/fertility.html Fertility Awareness, Food, and Night-Lighting]". Wise Traditions in Food, Farming and the Healing Arts, Spring 2004. See section on Night-Lighting.

[22] Harder, Ben. Bright nights kindle cancers in mice. Science News, Week of Aug. 28, 2004; Vol. 166, No. 9 , p. 141.

[23] Shannon, Marilyn. Fertility, Cycles, and Nutrition. Cincinnati, Ohio: The Couple to Couple League International, 2001. pp. 71–72.

[24] As cited by Adams, Cecil, "What's the link between the moon and menstruation?" (accessed 6 June 2006): Abell, George O.; Barry Singer (1983). Science and the Paranormal: Probing the Existence of the Supernatural, Scribner Book Company. ISBN 0-684-17820-6.

[25] Cutler WB. Lunar and menstrual phase locking. Am J Obstet Gynecol. 1980 Aug 1;137(7):834-9. PMID: 7405975.
Friedmann E. Menstrual and lunar cycles. Am J Obstet Gynecol. 1981 Jun 1;140(3):350. PMID: 7246643
Law SP. The regulation of menstrual cycle and its relationship to the moon. Acta Obstet Gynecol Scand. 1986;65(1):45-8. PMID: 3716780
Zimecki M. The lunar cycle: effects on human and animal behavior and physiology. Postepy Hig Med Dosw (Online). 2006;60:1–7. Review. PMID: 16407788

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v·d·e Physiology, endocrinology, sex: Reproductive physiology and endocrinology
Menstrual cycle/Estrous cycle	Menstruation - Follicular phase - Ovulation - Luteal phase
Gametogenesis	Spermatogenesis -Oogenesis
Sexuality	Human sexual behavior - Sexual intercourse - Erection - Ejaculation - Orgasm - Insemination - Fertilisation/Fertility - Masturbation - Pregnancy - Postpartum period
Lifespan	Prenatal development - Sexual dimorphism - Sexual differentiation - Puberty (Menarche, Adrenarche) - Maternal age/Paternal age - Climacteric (Menopause, Andropause)
Eggs	Oviposition - Oviparity - Ovoviviparity - Viviparity

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+{{BioPsy}}
-[[Image:MenstrualCycle.png|thumb|300px|right|Menstrual cycle......]]
+{{Expert}}
+[[Image:MenstrualCycle2.png|thumb|300px|right|Menstrual cycle]]
-The '''menstrual cycle''' is a recurring cycle of [[physiology|physiological]] changes in the females of some animal species that is associated with reproductive fertility.
-This article concentrates on the menstrual cycle as it occurs in [[human beings]].
+The '''menstrual cycle''' is a recurring cycle of [[physiology|physiological]] changes that occurs in the females of several mammals, including [[human beings]] and other [[ape]]s.<!--
+ --><ref>{{cite encyclopedia | title = ape | encyclopedia = Encyclopædia Britannica | volume = Britannica Concise Encyclopedia | date = 2007 | url = http://concise.britannica.com/ebc/article-9309760/apes | accessdate = 2007-08-03 }}</ref>  Humans are the only species that has a menstrual cycle with [[#Hidden ovulation|concealed ovulation]].  Other [[Eutheria|placental mammals]] experience an [[Estrous cycle|estrous]], where imminent ovulation is signaled to the males of the species.
+The menstrual cycle is under the control of the [[hormone]] system and is necessary for [[reproduction]].  This article concentrates on the menstrual cycle as it occurs in human beings.
 == Overview ==
+A woman's first [[menstruation]] is termed ''[[menarche]]'', and is one of the later stages of [[puberty]] in girls.  The average age of menarche in humans is 12 years, but is normal anywhere between ages 8 and 16. Factors such as heredity, diet and overall health can accelerate or delay menarche.<!--
-Only [[human beings]] and the [[Hominidae|great apes]] experience a true menstrual cycle. Most [[placenta|placental]] [[mammal]]s experience [[estrus]] instead. The menstrual cycle is under the control of the [[reproduction|reproductive]] [[hormone]] system and is necessary for [[reproduction]]. In women, menstrual cycles occur typically on a monthly basis between [[puberty]] and [[menopause]].
+  --><ref name="age">"[http://www.4woman.gov/faq/menstru.htm#6 At what age does a girl get her first period?]," from ''Menstruation and the Menstrual Cycle'', National Women's Health Information Center (accessed June 11, 2005)</ref> The cessation of menstrual cycles at the end of a woman's reproductive life is termed [[menopause]]. The average age of menopause in women is 51 years, with anywhere between 40 and 58 being common.  Menopause before age 35 is considered ''premature''.  The age of menopause is largely a result of genetics; however, illness, certain surgeries, or medical treatments may cause menopause to occur earlier.<!--
+ --><ref>{{cite web | last = Shuman | first = Tracy | title = Your Guide to Menopause | work = WebMD |date=February 2006 | url = http://www.webmd.com/content/article/9/2953_504.htm | accessdate = 2006-12-16 }}</ref>
+The length of a woman's menstrual cycle will typically vary, with some shorter cycles and some longer cycles. A woman who experiences variations of less than eight days between her longest cycles and shortest cycles is considered to have regular menstrual cycles. It is unusual for a woman to experience cycle length variations of less than four days.  Length variation between eight and 20 days is considered moderately irregular. Variation of 21 days or more between a woman's shortest and longest cycle lengths is considered very irregular (see [[#Cycle abnormalities|cycle abnormalities]]).<!--
-During the menstrual cycle, the sexually mature female body builds up the lining of the uterus with gradually increasing amounts of [[estrogen]], and when this hormone reaches a critical level, [[estradiol]] is produced, and shortly thereafterward there is the stimulation of the ovaries with [[Follicle Stimulating Hormone]], and [[luteinizing hormone]]. Follicles begin developing, and within a few days one "matures" into an [[Ovum|ovum or egg]]. The ovary then releases this egg, (or occasionally two, which might result in [[zygote|dizygotic]], or non-identical, [[twins]]) at the time of [[ovulation]]. The lining of the [[uterus]], the [[endometrium]], peaks shortly there afterward in a synchronised fashion. After [[ovulation]], this lining changes to prepare for potential [[conception]] and [[implantation]] of the fertilized egg to establish a [[pregnancy]]. The hormone [[progesterone]] rises after ovulation, and peaks shortly thereafter.
+ --><ref name="kippley">{{cite book | first=John | last=Kippley | coauthors=Sheila Kippley | year=1996 | title=The Art of Natural Family Planning | edition=4th Edition | publisher=The Couple to Couple League | location=Cincinnati, OH | id=ISBN 0-926412-13-2 | pages=p. 92 }}</ref>
+Menstrual cycles are counted from the first day of menstrual bleeding, because the onset of menstruation corresponds closely with the hormonal cycle. The menstrual cycle may be divided into several phases, and the length of each phase varies from woman to woman and cycle to cycle.  Average values are shown below:
-If fertilization and pregnancy do not ensue, the uterus sheds the lining, culminating with [[menstruation]], which marks the low point for [[estrogen]] activity. This manifests itself to the outer world in the form of the '''menses''' (also ''menstruum''): essentially part of the endometrium and blood products that pass out of the body through the [[vagina]]. Although this is commonly referred to as ''blood'', it differs in composition from [[venous blood]]. Menstrual cycles are counted from the beginning of menstruation, because this is an outside sign that corresponds closely with the hormonal cycle. Menses, or bleeding and other menstrual signs may end at different points in the new cycle.
+{| class="wikitable"
+| '''Name of phase''' || '''Days'''
+ |-
+ | menstrual phase || 1–4
+ |-
+ | follicular phase (also known as proliferative phase) || 5–13
+ |-
+ | ovulation (not a phase, but an event dividing phases) || 14
+ |-
+ | luteal phase (also known as secretory phase) || 15–26
+ |-
+ | ischemic phase (some sources group this with secretory phase) || 27–28
+|}
+During the follicular phase the [[Endometrium|lining]] of the [[uterus]] thickens, stimulated by gradually increasing amounts of [[estrogen]]. Follicles in the [[ovary]] begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two follicles become dominant (non-dominant follicles atrophy and die). The dominant follicle releases an [[Ovum|ovum or egg]] in an event called [[ovulation]]. (An egg that is fertilized by a [[spermatozoon]] will become a [[Fertilisation|zygote]], taking one to two weeks to travel down the [[fallopian tube]]s to the uterus. If the egg is not fertilized within about a day of ovulation, it will die and be absorbed by the woman's body<ref>http://www.americanpregnancy.org/gettingpregnant/understandingovulation.html</ref>.) After ovulation the remains of the dominant follicle in the ovary become a [[corpus luteum]]; this body has a primary function of producing large amounts of [[progesterone]]. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a [[pregnancy]]. If implantation does not occur within approximately two weeks, the corpus luteum will die, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining in a process termed menstruation.
-Common usage refers to menstruation and menses as a '''period'''. This bleeding serves as a sign that a woman has not become [[pregnancy|pregnant]]. (However, this cannot be taken as certainty, as sometimes there is some bleeding in early pregnancy.)  During the reproductive years, failure to menstruate may provide the first indication to a [[woman]] that she may have become pregnant. A woman might say that her "period is late"  when an expected menstruation has not started and she might have become pregnant.
+==Phases of the menstrual cycle==
-Menstruation forms a normal part of a natural cyclic process occurring in healthy women between [[puberty]] and the end of the reproductive years. The onset of menstruation, known as ''[[menarche]]'', occurs at an average age of 12, but is normal anywhere between 8 and 16. Factors such as heredity, diet and overall health can accelerate or delay the onset of menarche.<!--
+===Menstruation===
-  --><ref name="age">"[http://www.4woman.gov/faq/menstru.htm#6 At what age does a girl get her first period?]," from ''Menstruation and the Menstrual Cycle'', National Women's Health Information Center (accessed June 11, 2005)</ref>
+{{main|Menstruation}}
+Menstruation is also called menstrual bleeding, '''menses''', a '''period''' or '''catamenia'''. This bleeding normally serves as a sign that a woman has not become [[pregnancy|pregnant]]. (However, this cannot be taken as certainty, as sometimes there is some bleeding in early pregnancy.)  During the reproductive years, failure to menstruate may provide the first indication to a [[woman]] that she may have become pregnant. A woman might say that her "period is late"  when an expected menstruation has not started and she might have become pregnant.
+''Eumenorrhea'' denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).<!--
-The condition [[precocious puberty]] has caused menstruation to occur in girls as young as 8 months old.<!--
- --><ref>{{cite web | last = Mikkelson | first = Barbara | coauthors = David P. Mikkelson | title = Youngest Mother | work = Snopes.com | date = 2004-07-21 | url = http://www.snopes.com/pregnant/medina.asp | accessdate = 2006-07-02 }}</ref> Some women experience their first period in their late teens. The last period, [[menopause]], usually occurs between the ages of 45 and 55. Deviations from this pattern deserve medical attention. [[Amenorrhea]] refers to a prolonged absence of menses during the reproductive years of a woman for reasons other than pregnancy. For example, women with very low [[body fat]], such as [[athlete]]s, may cease to menstruate. The presence of menstruation does not prove that ovulation took place; women who do not ovulate may have menstrual cycles. Those [[anovulatory cycle]]s tend to take place less regularly and show greater variation in cycle length. In addition, the absence of menstruation also does not prove that ovulation did not take place, because hormone disruptions in non-pregnant women can suppress bleeding on occasion.
-== The normal menstrual cycle in humans ==
-Women show considerable variation in the lengths of their menstrual cycles, and the length of the menstrual cycle differs in different animals (see below).
-While cycle length may vary, 28 days is generally taken as representative of the average ovulatory cycle in women. Convention uses the onset of menstrual bleeding to mark the beginning of the cycle, so the first day of bleeding is called "Cycle Day one".
-One can divide the menstrual cycle into four phases:
-===Menstruation===
-''Eumenorrhea'' denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal.<!--
   --><ref name="US-typical">>{{cite web | author=The National Women's Health Information Center | title=What is a typical menstrual period like?|url=http://www.4woman.gov/faq/menstru.htm#4 | year=November 2002 |  publisher=U.S. Department of Health and Human Services | accessdate=2005-06-11}}</ref>
-The average blood loss during menstruation is [[1 E-5 m3|35 millilitres]] with 10-80 mL considered normal;<!--
+The average blood loss during menstruation is [[1 E-5 m3|35 millilitres]] with 10–80 mL considered normal;<!--
-  --><ref name="">{{cite web | author=David L Healy | title=Menorrhagia Heavy Periods - Current Issues | year=2004-11-24 | publisher=Monash University | id=ABN 12 377 614 012 | url=http://www.med.monash.edu.au/ob-gyn/research/menorr/}}</ref>
+  --><ref name="">{{cite web | author=David L Healy | title=Menorrhagia Heavy Periods - Current Issues | year=2004-11-24 | publisher=Monash University | id=ABN 12 377 614 012 | url=http://www.med.monash.edu.au/ob-gyn/research/menorr.html}}</ref>
-many women also notice shed [[endometrium]] lining that appears as tissue mixed with the blood. An [[enzyme]] called [[plasmin]] &mdash; contained in the endometrium &mdash; inhibits the blood from [[blood clotting|clotting]]. Because of this blood loss, women have higher dietary requirements for [[iron]] than do males to prevent [[iron deficiency (medicine)|iron deficiency]]. Many women experience [[uterine]] cramps, also referred to as [[dysmenorrhea]], during this time. A vast industry has grown to provide [[#Menstrual products|sanitary products]] to help women to manage their menses.
+many women also notice shedding of the [[endometrium]] lining that appears as tissue mixed with the blood. An [[enzyme]] called [[plasmin]] &mdash; contained in the endometrium &mdash; tends to inhibit the blood from [[blood clotting|clotting]]. Because of this blood loss, women have higher dietary requirements for [[iron]] than do males to prevent [[iron deficiency (medicine)|iron deficiency]]. Many women experience [[uterine]] cramps during this time (severe cramps or other symptoms are called [[dysmenorrhea]]).  A vast industry of [[Menstruation#Menstrual products|sanitary products]] has grown to help women during their menstruation.
 ===Follicular phase===
+{{main|Follicular phase}}
-Through the influence of a rise in [[Follicle stimulating hormone]] (FSH), five to seven tertiary-stage [[ovarian follicle]]s are recruited for entry into the menstrual cycle. These follicles, that have been growing for the better part of a year in a process known as [[folliculogenesis]], compete with each other for dominance. In a signal cascade kicked off by [[luteinizing hormone]] (LH), the follicles secrete [[estradiol]], a steroid that acts to inhibit pituitary secretion of FSH. With diminished FSH supply comes a slowing in growth that eventually leads to follicle death, known as ''atresia''. The largest follicle secretes [[inhibin]] that serves as a finishing blow to less competent follicles by further suppressing FSH. This ''dominant follicle'' continues growing, forms a bulge near the surface of the ovary, and soon becomes competent to ovulate.
+Through the influence of a rise in [[follicle stimulating hormone]] (FSH), five to seven tertiary-stage [[ovarian follicle]]s are recruited for entry into the next menstrual cycle. These follicles, that have been growing for the better part of a year in a process known as [[folliculogenesis]], compete with each other for dominance.  Under the influence of several hormones, all but one of these follicles will undergo ''atresia'', while one (or occasionally two) dominant follicles will continue to maturity.   As they mature, the follicles secrete increasing amounts of [[estradiol]], an [[oestrogen]].
-The follicles also secrete [[estrogen]]s (of which estradiol is a member). Estrogens initiate the formation of a new layer of endometrium in the uterus, histologically identified as the proliferative endometrium. If fertilized, the [[embryo]] will implant itself within this hospitable flesh.
+The [[oestrogen]]s that follicles secrete, initiate the formation of a new layer of [[endometrium]] in the uterus, histologically identified as the proliferative endometrium. The estrogen also stimulates crypts in the [[cervix]] to produce fertile cervical mucus, which may be noticed by women practicing [[fertility awareness]].
 ===Ovulation===
 {{main|Ovulation}}
-[[image:ovulation.jpg|thumb|This ovary is about to release an egg.]]
+[[Image:ovulation.jpg|thumb|An ovary about to release an egg.]]
-When the follicle has matured, it secretes enough estradiol to trigger the acute release of [[luteinizing hormone]] (LH). In the average cycle this LH surge starts around cycle day 12 and may last 48 hours. The release of LH matures the egg and weakens the wall of the follicle in the ovary. This process leads to [[ovulation]]: the release of the now mature [[ovum]], the largest cell of the body (with a diameter of about [[1 E-4 m|0.5 mm]]). Which of the two ovaries &mdash; left or right &mdash; ovulates appears essentially random; no known left/right co-ordination exists. The [[Fallopian tube]] needs to capture the egg and provide the site for [[fertilization]]. A characteristic clear and stringy [[mucus]] exhibiting [[spinnbarkeit]] develops at the [[cervix]], ready to accept [[sperm]] from [[intercourse]]. In some women, ovulation features a characteristic pain called ''[[Mittelschmerz]]'' (German term meaning 'middle pain') which lasts for several hours. The sudden change in hormones at the time of ovulation also causes light mid-cycle bleeding for some women. Many women perceive the vaginal and cervical mucus changes at ovulation, particularly if they are monitoring themselves for [[Fertility awareness|signs of fertility]]. An unfertilized egg will eventually disintegrate or dissolve in the uterus. Scientific investigations have indicated that the [[olfactory]] acuity or the sense of [[olfaction|smell]] is greatest during ovulation in women.<!--
+When the egg has matured, it secretes enough estradiol to trigger the acute release of [[luteinizing hormone]] (LH). In the average cycle this LH surge starts around cycle day 12 and may last 48 hours. The release of LH matures the egg and weakens the wall of the follicle in the ovary. This process leads to [[ovulation]]: the release of the now mature [[ovum]], the largest cell of the body (with a diameter of about [[1 E-4 m|0.5 mm]]). Which of the two ovaries &mdash; left or right &mdash; ovulates appears essentially random; no known left/right co-ordination exists. The [[Fallopian tube]] needs to capture the egg and provide the site for [[fertilization]]. In some women, ovulation features a characteristic pain called ''[[mittelschmerz]]'' (German term meaning 'middle pain') which may last a few hours. The sudden change in hormones at the time of ovulation also causes light mid-cycle bleeding for some women. An unfertilized egg will eventually disintegrate or dissolve in the uterus.
-  --><ref name="threshold">{{cite journal | author=Navarrete-Palacios E, Hudson R, Reyes-Guerrero G, Guevara-Guzman R | title=Lower olfactory threshold during the ovulatory phase of the menstrual cycle | journal=Biol Psychol | year=2003 | pages=269-79 | volume=63 | issue=3 | id=PMID 12853171}}</ref>
 ===Luteal phase===
+{{main|Luteal phase}}
-The corpus luteum is the solid body formed in the ovaries after the egg has been released from the fallopian tube which continues to grow and divide for a while. After ovulation, the residual follicle transforms into the [[corpus luteum]] under the support of the pituitary hormones. This corpus luteum will produce [[progesterone]] in addition to estrogens for approximately the next 2 weeks. Progesterone plays a vital role in converting the proliferative endometrium into a secretory lining receptive for [[implantation]] and supportive of the early [[pregnancy]]. It raises the body temperature by one-half to one degree Fahrenheit (one-quarter to one-half degree Celsius), thus women who record their temperature on a daily basis will notice that they have entered the luteal phase. If fertilization of an egg has occurred, it will travel as an early [[blastocyst]] through the fallopian tube to the uterine cavity and implant itself 6 to 12 days after ovulation. Shortly after implantation, the growing embryo will signal its existence to the maternal system. One very early signal consists of [[human chorionic gonadotropin]] ([[hCG]]), a hormone that [[pregnancy test]]s can measure. This signal has an important role in maintaining the corpus luteum and enabling it to continue to produce progesterone. In the absence of a pregnancy and without hCG, the corpus luteum demises and inhibin and progesterone levels fall. This will set the stage for the next cycle. Progesterone withdrawal leads to menstrual shedding (''progesterone withdrawal bleeding''), and falling inhibin levels allow FSH levels to rise to raise a new crop of follicles.
+The corpus luteum is the solid body formed in the ovaries after the egg has been released into the fallopian tube which continues to grow and divide for a while. After ovulation, the residual follicle transforms into the [[corpus luteum]] under the support of the pituitary hormones. This corpus luteum will produce [[progesterone]] in addition to estrogens for approximately the next 2 weeks. Progesterone plays a vital role in converting the proliferative endometrium into a secretory lining receptive for [[implantation]] and supportive of the early [[pregnancy]]. It raises the body temperature by one-half to one degree Fahrenheit (one-quarter to one-half degree Celsius), thus women who record their temperature on a daily basis will notice that they have entered the luteal phase. If fertilization of an egg has occurred, it will travel as an early [[blastocyst]] through the fallopian tube to the uterine cavity and implant itself 6 to 12 days after ovulation. Shortly after implantation, the growing embryo will signal its existence to the maternal system. One very early signal consists of [[human chorionic gonadotropin]] ([[hCG]]), a hormone that [[pregnancy test]]s can measure. This signal has an important role in maintaining the corpus luteum and enabling it to continue to produce progesterone. In the absence of a pregnancy and without hCG, the corpus luteum demises and inhibin and progesterone levels fall. This will set the stage for the next cycle. Progesterone withdrawal leads to menstrual shedding (''progesterone withdrawal bleeding''), and falling inhibin levels allow FSH levels to rise to raise a new crop of follicles.
-==Menstrual symptoms==
-In many women, various unpleasant symptoms caused by the involved hormones and by [[cramp]]ing of the uterus can precede or accompany menstruation. More severe symptoms may include significant menstrual pain ([[dysmenorrhea]]), abdominal pain, [[migraine]] headaches, [[depression (mood)|depression]] and irritability. Some women encounter [[premenstrual stress syndrome]] (PMS or premenstrual syndrome), severe cases of which are clinically referred to as [[premenstrual dysphoric disorder]] (PMDD). Other women are said to suffer from what some doctors call [[post-menstrual syndrome]] where similar symptoms manifest themselves. This is rare and is usually not as severe or as long as pre-menstrual syndrome. Breast discomfort caused by [[premenstrual water retention]] is very common. The list of symptoms experienced varies from person to person. Furthermore, within an individual, the severity of the symptoms may vary from cycle to cycle. Pharmaceutical and herbal companies provide [[#Menstrual products|products]] designed to lessen or relieve some or all of these symptoms.
 ==The fertile window==
-The length of the follicular phase &mdash; and consequently the length of the menstrual cycle &mdash; may vary widely. The luteal phase, however, almost always takes the same number of days. Some women have a luteal phase of 10 days, others of 16 days (the average is 14 days), but for each individual woman, this length will remain constant. [[Sperm]] survive inside a woman for 3 days on average, with survival time up to five days considered normal. A pregnancy resulting from sperm life of eight days has been documented.<!--
+The length of the follicular phase &mdash; and consequently the length of the menstrual cycle &mdash; may vary widely. The luteal phase, however, almost always takes the same number of days for each woman: Some women have a luteal phase of 10 days, others 16 days, while the average is 14 days. [[Spermatozoon|Sperm]] survive inside a woman for 3 days on average, with survival time up to five days considered normal. A pregnancy resulting from sperm life of eight days has been documented.<!--
   --><ref name="spermlife">{{cite journal | author=Ball M | title=A prospective field trial of the "ovulation method" of avoiding conception | journal=Eur J Obstet Gynecol Reprod Biol | year=1976 | pages=63-6 | volume=6 | issue=2 | id=PMID 985763}}</ref><!--
   --><ref name="Billings">{{cite web | author=Dr Evelyn Billings & Ann Westmore | title=Trials of The Billings Ovulation Method | year=2005 | url=http://www.woomb.org/bom/trials/index.html | accessdate=2005-11-03}}</ref><!-- split paper from this website where quoted
   --><ref name="JIndianMedAssoc1993-Billings">{{cite journal | author=Sinha G, Sinha A | title=A field trial of Billings' ovulation method for spacing and limitation of birth | journal=J Indian Med Assoc | year=1993 | pages=255-6 | volume=91 | issue=10 | id=PMID 8308307}}</ref> <!-- additional original source ref -->
-The most fertile period (the time with the highest likelihood of [[sexual intercourse]] leading to pregnancy) covers the time from some 5 days before ovulation until 1-2 days after ovulation. In an average 28 day cycle with a 14-day luteal phase, this corresponds to the second and the beginning of the third week of the cycle.
+The most fertile period (the time with the highest likelihood of pregnancy resulting from [[sexual intercourse]]) covers the time from some 5 days before ovulation until 1–2 days after ovulation. In an average 28 day cycle with a 14-day luteal phase, this corresponds to the second and the beginning of the third week of the cycle.
 [[Fertility awareness]] methods of [[birth control]] attempt to determine the precise time of ovulation in order to find the relatively fertile and the relatively infertile days in the cycle.
-People who have heard about the menstrual cycle and ovulation may commonly and mistakenly assume, for [[contraceptive]] purposes, that menstrual cycles always take a regular 28 days, and that ovulation always occurs 14 days after beginning of the menses. This assumption may lead to unintended pregnancies. Note too that not every bleeding event counts as a menstruation, and this can mislead people in their calculation of the fertile window.
+People who have heard about the menstrual cycle and ovulation often mistakenly assume, for [[contraceptive]] purposes, that menstrual cycles regularly take 28 days, and that ovulation always occurs 14 days after beginning of the menses. This assumption may lead to unintended pregnancies. Note too that not every bleeding event counts as a menstruation, and this can mislead people in their calculation of the fertile window.
-If a woman wants to conceive, the most fertile time occurs between 19 and 10 days prior to the expected menses. Many women use ovulation detection kits that detect the presence of the LH surge in the urine to indicate the most fertile time. Other ovulation detection systems rely on observation of one or more of the three primary fertility signs (basal body temperature, cervical fluid, and cervical position).
+If a woman wants to conceive, the most fertile time occurs between 19 and 10 days prior to the expected menses. Many women use ovulation detection kits that detect the presence of the LH surge in the urine to indicate the most fertile time. Other ovulation detection systems rely on observation of one or more of the three primary fertility signs ([[basal body temperature]], cervical fluid, and cervical position).
 Among women living closely together, the onsets of menstruation may tend to synchronise somewhat. This [[McClintock effect]] was first described in 1971, and possibly explained by the action of [[pheromone]]s in 1998.<!--
   --><ref name="Mclintock">{{cite journal | author=Stern K, McClintock MK | title=Regulation of ovulation by human pheromones | journal=Nature | year=1998 | pages=177-9 | volume=392 | issue=6672 | id=PMID 9515961}}</ref>
-However, subsequent research has called this conclusion into question.
+However, subsequent research has called this conclusion into question.<!--
+ --><ref>{{cite web | last = Adams | first = Cecil | authorlink = Cecil Adams | title = Does menstrual synchrony really exist? | work = The Straight Dope | publisher = The Chicao Reader | date = [[2002-12-20]] | url = http://www.straightdope.com/columns/021220.html | accessdate = 2007-01-10 }}</ref>
 == Hormonal control ==
-Extreme intricacies regulate the menstrual cycle. For many years, researchers have argued over which regulatory system has ultimate control: the hypothalamus, the pituitary, or the ovary with its growing follicle; but all three systems have to interact. In any scenario, the growing follicle has a critical role: it matures the lining, provides the appropriate feedback to the hypothalamus and pituitary, and modifies the mucus changes at the cervix. Two [[sex hormone]]s play a role in the control of the menstrual cycle: [[estradiol]] and [[progesterone]]. While estrogen peaks twice, during follicular growth and during the luteal phase, progesterone remains virtually absent prior to ovulation, but becomes critical in the luteal phase and during pregnancy. Many tests for ovulation check for the presence of progesterone. These sex hormones come under the influence of the pituitary gland, and both FSH and LH play necessary roles. FSH stimulates immature [[follicle]]s in the ovaries to grow. LH triggers ovulation. The [[gonadotropin-releasing hormone]] of the hypothalamus controls the pituitary, yet both the pituitary and the hypothalamus receive feedback from the follicle. After ovulation the corpus luteum &mdash; which develops from the burst follicle and remains in the ovary &mdash; secretes both estradiol and progesterone. Only if pregnancy occurs do hormones appear in order to suspend the menstrual cycle, while production of estradiol and progesterone continues. Abnormal hormonal regulation leads to disturbance in the menstrual cycle.
+Extreme intricacies regulate the menstrual cycle. For many years, researchers have argued over which regulatory system has ultimate control: the hypothalamus, the pituitary, or the ovary with its growing follicle; but all three systems have to interact. In any scenario, the growing follicle has a critical role: it matures the lining, provides the appropriate feedback to the hypothalamus and pituitary, and modifies the mucus changes at the cervix.
+===Gonadal===
-Some women with [[Neurology|neurological conditions]] experience increased activity of their conditions at about the same time every month. 80 percent of women with [[epilepsy]] have more seizures than usual in the phase of their cycle when progresterone declines and estrogen increases.
+Two [[sex hormone]]s play a role in the control of the menstrual cycle: [[estradiol]] and [[progesterone]]:
+* Estrogen peaks twice, during follicular growth and during the luteal phase.
+* Progesterone remains virtually absent prior to ovulation, but becomes critical in the luteal phase and during pregnancy. Many tests for ovulation check for the presence of progesterone.
+After ovulation the [[corpus luteum]] &mdash; which develops from the burst follicle and remains in the ovary &mdash; secretes both estradiol and progesterone. Only if pregnancy occurs do hormones appear in order to suspend the menstrual cycle, while production of estradiol and progesterone continues. Abnormal hormonal regulation leads to disturbance in the menstrual cycle.
-Mice have been used as an experimental system to investigate possible mechanisms by which levels of sex steroid hormones might regulate nervous system function. During the part of the mouse estrous cycle when progesterone is highest, the level of [[Neuron|nerve-cell]] [[GABA A receptor|GABA receptor]] subtype delta was high. Since these GABA receptors are [[Inhibitory postsynaptic potential|inhibitory]], nerve cells with more delta receptors are less likely to fire than cells with lower numbers of delta receptors. During the part of the mouse estrous cycle when estrogen levels are higher than progesterone levels, the number of delta receptors decrease, increasing nerve cell activity, in turn increasing anxiety and seizure susceptibility.<!--
-  --><ref name="Maguire">{{cite journal | author=Maguire, J.L. . . . and I. Mody. | title=[http://www.nature.com/neuro/journal/v8/n6/abs/nn1469.html Ovarian cycle-linked changes in GABA<sub>A</sub> receptors mediating tonic inhibition alter seizure susceptibility and anxiety] | journal=Nature Neuroscience | volume=8 | issue=June | year=2005 | pages=797-804}}</ref>
+===Hypothalamus and pituitary===
+These sex hormones come under the influence of the pituitary gland, and both FSH and LH play necessary roles:
+* FSH stimulates immature [[follicle]]s in the ovaries to grow.
+* LH triggers ovulation.
+The [[gonadotropin-releasing hormone]] of the hypothalamus controls the pituitary, yet both the pituitary and the hypothalamus receive feedback from the follicle.
+===Cyclic effects upon nervous system===
+Some women with [[Neurology|neurological conditions]] experience increased activity of their conditions at about the same time every month. 80 percent of women with [[epilepsy]] have more seizures than usual in the phase of their cycle when progesterone declines and estrogen increases.
+Mice have been used as an experimental system to investigate possible mechanisms by which levels of sex steroid hormones might regulate nervous system function. During the part of the mouse oestrous cycle when progesterone is highest, the level of [[Neuron|nerve-cell]] [[GABA A receptor|GABA receptor]] subtype delta was high. Since these GABA receptors are [[Inhibitory postsynaptic potential|inhibitory]], nerve cells with more delta receptors are less likely to fire than cells with lower numbers of delta receptors. During the part of the mouse estrous cycle when estrogen levels are higher than progesterone levels, the number of delta receptors decrease, increasing nerve cell activity, in turn increasing anxiety and seizure susceptibility.<!--
+  --><ref name="Maguire">{{cite journal | author=Maguire, J.L. . . . and I. Mody. | title=[http://www.nature.com/neuro/journal/v8/n6/abs/nn1469.html Ovarian cycle-linked changes in GABA<sub>A</sub> receptors mediating tonic inhibition alter seizure susceptibility and anxiety] | journal=Nature Neuroscience | volume=8 | issue=June | year=2005 | pages=797–804}}</ref>
 ==Hidden ovulation==
 {{main|Concealed ovulation}}
-Unlike almost all other species, the external physical changes of a human female near ovulation are very subtle. A woman may sense her own ovulation while it may remain indiscernible to others; this is considered to have [[sociobiology|sociobiological]] significance. In contrast, other species often signal receptivity through heat. The great apes are the only other mammals to have hidden ovulation.
+Unlike almost all other species, the external physical changes of a human female near ovulation are very subtle. A woman may sense her own ovulation while it may remain indiscernible to others; this is considered to have [[sociobiology|sociobiological]] significance. In contrast, other species often signal receptivity through heat, swellings, and/or changes in color in the genital area. Humans are the only mammal to have hidden ovulation, although some argue that the extended estrus period of the [[bonobo]] (reproductive-age females are in heat for 75% of their menstrual cycle)<!--
+ --><ref>{{cite book |author=Lanting, Frans; Waal, F. B. M. de |title=Bonobo: the forgotten ape |publisher=University of California Press |location=Berkeley |year=1997 |pages=p.107 |isbn=0-520-20535-9 |url=http://www.serpentfd.org/a/dewall1997.html |accessdate=2007-09-05 }}</ref> has a similar effect to the lack of a "heat" in human females.<!--
+ --><ref>{{cite journal | last = Stanford | first = Craig B. | title =  The Brutal Ape vs. the Sexy Ape? The Make-Love-Not-War Ape  | journal = American Scientist | volume = 88 | issue = 2 | pages = 110 | date = March-April 2000 | url = http://www.americanscientist.org/template/AssetDetail/assetid/14721/page/2;jsessionid=baa9 | doi = 10.1511/2000.2.110 | accessdate = 2007-09-05 }}</ref>
 ==The ovary as an egg-bank==
-Evidence suggests that eggs are formed from germ cells early in fetal life. The number is reduced to an estimated 400,000 to 450,000 immature eggs residing in each ovary at puberty. The menstrual cycle, as a biologic event, allows for ovulation of one egg typically each month. Thus over her lifetime a woman will ovulate approximately 400 to 450 times. All the other eggs dissolve by a process called [[atresia]]. As a woman's total egg supply is formed in fetal life, to be ovulated decades later, it has been suggested that this long lifetime may make the chromatin of eggs more vulnerable to division problems, breakage, and mutation than the chromatin of sperm, which are produced continuously during a man's reproductive life. This possibility is supported by the observation that fetuses and infants of older mothers have higher rates of chromosome abnormalities than those of older fathers.
+Evidence suggests that eggs are formed from germ cells early in fetal life. The number is reduced to an estimated 400,000 to 450,000 immature ova residing in each ovary at puberty. The menstrual cycle, as a biologic event, allows for ovulation of one egg typically each month. Thus over her reproductive lifetime a woman will ovulate approximately 400 to 450 times. All the other eggs dissolve by a process called [[atresia]]. As a woman's total egg supply is formed in fetal life,<!--
+ --><ref>{{cite web | last = Krock | first = Lexi | title = Fertility Throughout Life | work = 18 Ways to Make a Baby | publisher = NOVA Online |date=October 2001 | url = http://www.pbs.org/wgbh/nova/baby/fert_text.html | accessdate = 2006-12-24 }}
+{{cite web | last = Haines | first = Cynthiac | title = Your Guide to the Female Reproductive System | work = The Cleveland Clinic Women's Health Center | publisher = WebMD | date = January 2006 | url = http://www.webmd.com/content/article/51/40619.htm | accessdate = 2006-12-24 }}</ref> to be ovulated decades later, it has been suggested that this long lifetime may make the [[chromatin]] of eggs more vulnerable to division problems, breakage, and mutation than the chromatin of sperm, which are produced continuously during a man's reproductive life.
-== The anovulatory menstrual cycle==
-Not all menstruations result from an ovulatory menstrual cycle ([[Anovulatory cycle]] - literally 'an-' absence of 'ovulation'). In some women, follicular development may start but not complete, nevertheless estrogens will form and will stimulate the uterine lining. Sooner or later the uterus will shed this lining. As no ovulation and no progesterone involvement occurs, doctors call this type of bleeding an ''estrogen breakthrough bleeding'', and cannot always predict its duration or frequency. Anovulatory bleeding commonly occurs prior to [[menopause]] (premenopause) or in women with [[polycystic ovary syndrome]]. Infrequent or irregular ovulation is called ''oligoovulation''.
 ==Cycle abnormalities==
 {{main|Menstrual disorder}}
+===Anovulation===
+Apparently normal menstrual bleeding can occur without ovulation preceding it ([[anovulatory cycle]] - "an-" meaning "absence of" +ovulation). In some women, follicular development may start but not be completed; nevertheless, estrogens will form and will stimulate the uterine lining. Anovulatory bleeding resulting from a very thick endometrium caused by prolonged, continued high estrogen levels is called ''estrogen breakthrough bleeding''. Anovulatory bleeding triggered by a sudden drop in estrogen levels is called ''estrogen withdrawal bleeding''.<!--
+ --><ref name="tcoyf">{{cite book | first=Toni | last=Weschler | year=2002 | title=Taking Charge of Your Fertility | pages=p.107 | edition=Revised Edition | publisher=HarperCollins | location=New York | id=ISBN 0-06-093764-5 }}</ref>
+Anovulatory bleeding may occur on a regular basis, but more commonly happens with irregular frequency. Anovulatory bleeding commonly occurs prior to [[menopause]] (premenopause) or in women with [[polycystic ovary syndrome]].
-===Frequency===
-The "normal menstrual cycle" occurs every 28 days ± 7 days.
+Infrequent or irregular ovulation is called ''oligoovulation''.
-The medical term for cycles with intervals of 21 days or fewer is ''[[polymenorrhea]]'' and, on the other hand, the term for cycles with intervals exceeding 35 days is ''[[oligomenorrhea]]'' (or ''[[amenorrhea]]'' if intervals exceed 180 days).
 ===Flow===
-The normal menstrual flow amounts to 50 mL ± 30 mL. It follows a "crescendo-decrescendo" pattern; that is, it starts at a moderate level, increases somewhat, and then slowly tapers. Sudden heavy flows or amounts in excess of 80 mL (''hypermenorrhea'' or ''[[menorrhagia]]'') may stem from hormonal disturbance, uterine abnormalities, including uterine [[leiomyoma]] or [[cancer]], and other causes. Doctors call the opposite phenomenon, of bleeding very little, ''hypomenorrhea''.
+Sudden heavy flows or amounts in excess of 80 mL (''hypermenorrhea'' or ''[[menorrhagia]]'') are not normal.
+Bleeding very little (less than 10mL) is called ''hypomenorrhea''.
-===Duration===
-The typical woman bleeds ("is on her period") for three to seven days out of each month.
 Prolonged bleeding (''metrorrhagia'', also ''meno-metrorrhagia'') no longer shows a clear interval pattern. [[Dysfunctional uterine bleeding]] refers to hormonally caused bleeding abnormalities, typically anovulation.
-All these bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant patients may bleed, a [[pregnancy test]] forms part of the evaluation of abnormal bleeding.
+All bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant patients may bleed, a [[pregnancy test]] forms part of the evaluation of abnormal bleeding.
-==The birth control pill==
-{{main|Birth control pill}}
+===Cycle length===
-Estrogens and progesterone-like hormones make up the main active ingredients of [[birth control pill]]s. Typically they tend to mimic a menstrual cycle in appearance, but to suppress the critical event of the ovulatory cycle, namely ovulation. Normally, a woman takes hormone pills for 21 days, followed by 7 days of non-functional sugar pills or no pills at all; then the cycle starts again. During the 7 placebo days, a ''withdrawal bleeding'' occurs; this differs from ordinary menstruation, and skipping the placebos and continuing with the next batch of hormone pills may suppress it. (Two main versions of the pill exist: ''monophasic'' and ''triphasic''. With triphasic pills, skipping of the placebos and continuing with the next month's dose can make a woman more likely to experience spotting or breakthrough bleeding.) In 2003 the United States [[Food and Drug Administration]] (FDA) approved low-dose monophasic birth control pills which induce withdrawal bleedings only every 3 months.
+The medical term for cycles with intervals of 21 days or fewer is ''[[polymenorrhea]]'' and, on the other hand, the term for cycles with intervals exceeding 35 days is ''[[oligomenorrhea]]'' (or ''[[amenorrhea]]'' if intervals exceed 180 days).
+[[Amenorrhea]] refers to a prolonged absence of menses during the reproductive years of a woman. For example, women with very low [[body fat]], such as [[sportsperson|athlete]]s, may cease to menstruate. Amenorrhea also occurs during pregancy.
-== Etymology and the lunar month ==
-The terms "menstruation" and "menses" come from the [[Latin]] ''mensis'' (month), which in turn relates to the [[Greek language|Greek]] ''mene'' (moon) and to the roots of the English words ''month'' and ''moon'' &mdash; reflecting the fact that the [[moon]] also takes close to 28 days to revolve around the Earth (actually 27.32 days). The synodical [[lunar month]], the period between two new moons (or full moons), is 29.53 days long.
+===Early menarche===
-A 1975 book by Louise Lacey documented the experience of herself and 27 of her friends, who found that when they removed all artificial nightlighting their menstrual cycles began to occur in rhythm with the lunar cycle. She dubbed the technique [[Lunaception]].<ref>Lacey, Louise. ''Lunaception: A Feminine Odyssey into Fertility and Contraception''. New York: Coward, McCann & Geoghegan, 1975.</ref> Later studies in both humans<ref>Singer, Katie. "[http://www.westonaprice.org/women/fertility.html Fertility Awareness,
+The condition [[precocious puberty]] has caused menstruation to occur in girls as young as eight months old.<!--
-Food, and Night-Lighting]". ''Wise Traditions in Food, Farming and the Healing Arts'', Spring 2004. See section on Night-Lighting.</ref> and animals<ref>Harder, Ben. ''Bright nights kindle cancers in mice''. ''Science News'', Week of Aug. 28, 2004; Vol. 166, No. 9 , p. 141.</ref> have found that artificial light at night does influence the menstrual cycle in humans and the estrus cycle in mice (cycles are more regular in the absence of artificial light at night), though none have duplicated the synchronization of women's menstrual cycles with the lunar cycle. One author has suggested that sensitivity of women's cycles to nightlighting is caused by nutritional deficiencies of certain vitamins and minerals.<ref>Shannon, Marilyn.  ''Fertility, Cycles, and Nutrition''. Cincinnati, Ohio: The Couple to Couple League International, 2001. pp. 71-72.</ref>
+ --><ref>{{cite web | last = Mikkelson | first = Barbara | coauthors = David P. Mikkelson | title = Youngest Mother | work = Snopes.com | date = 2004-07-21 | url = http://www.snopes.com/pregnant/medina.asp | accessdate = 2006-07-02 }}</ref>
+==Contraception and menstruation==
-Some have suggested that the fact that other animals' menstrual cycles appear to be greatly different from lunar cycles (see [[#Menstruation in other mammals|Menstruation in other mammals]] below) is evidence that the average length of humans' cycle is most likely a coincidence.<ref>As cited by Adams, Cecil, [http://www.straightdope.com/classics/a990924.html "What's the link between the moon and menstruation?"] (accessed [[6 June]] [[2006]]): {{cite book | last = Abell | first = George O. | authorlink = George Ogden Abell | coauthors = Barry Singer | year = 1983 | title = Science and the Paranormal: Probing the Existence of the Supernatural | publisher = Scribner Book Company | id = ISBN 0684178206}}</ref><ref>Cutler WB. Lunar and menstrual phase locking. Am J Obstet Gynecol. 1980 Aug 1;137(7):834-9. PMID: 7405975.<br />Friedmann E. Menstrual and lunar cycles. Am J Obstet Gynecol. 1981 Jun 1;140(3):350. PMID: 7246643<br /> 	Law SP. The regulation of menstrual cycle and its relationship to the moon. Acta Obstet Gynecol Scand. 1986;65(1):45-8. PMID: 3716780<br />Zimecki M. [http://www.phmd.pl/modules.php?name=Current_Issue&d_op=downloadPMID&id=8121 The lunar cycle: effects on human and animal behavior and physiology.] Postepy Hig Med Dosw (Online). 2006;60:1-7. Review.
+===Hormonal options===
-PMID: 16407788</ref>
+{{main|Hormonal contraception}}
+Estrogens and progesterone-like hormones make up the main active ingredients of hormonal birth control methods such as the [[combined oral contraceptive pill|the pill]]. Typically they cause regular monthly bleeding that roughly mimics a menstrual cycle in appearance, but suppresses ovulation. With most pills, a woman takes hormone pills for 21 days, followed by 7 days of non-functional placebo pills or no pills at all, then the cycle starts again. During the 7 placebo days, a ''withdrawal bleeding'' occurs; this differs from ordinary menstruation, and skipping the placebos and continuing with the next batch of hormone pills may suppress it. (There are two main versions of the pill: ''monophasic'' and ''triphasic''. With triphasic pills, skipping placebos and continuing with the next month's dose can make a woman more likely to experience spotting or breakthrough bleeding.) In 2003, the U.S. [[Food and Drug Administration]] (FDA) approved low-dose monophasic birth control pills that induce withdrawal bleeding every 3 months. Yet another version of the pill is the Loestrin Fe, which has only a four-day placebo "week" (the placebos are actually iron supplements intended to replenish iron lost by bleeding); the other three placebos are replaced with active hormone pills. This system is intended to help shorten periods. [[Mircette]] contains several days of estrogen-only pills in addition to the usual combination estrogen/progestin pills, in the case of women who may have problems with low estrogen during the placebo days with other pills.
+Other types of hormonal birth control which affect menstruation include the vaginal [[Nuvaring]] and the transdermal [[Ortho Evra|patch]] (like the standard pill pack, it is used for three weeks, followed by a one-week break for bleeding) and the [[Depo Provera|injection]] (which can eliminate bleeding for three months at a time).
-== Menstrual products==
-While some women allow their menses to flow freely or learn to recognise when their menses will flow, most women prefer to use some artificial means to absorb or catch their menses to prevent soiling their clothes. There are a number of different methods used:
+===Effects on menstruation===
-*[[Sanitary napkin]]s (Sanitary towels) or pads - Somewhat rectangular pieces of material worn in the underpants to absorb menstrual flow, often with "wings," pieces that fold around the [[Undergarment|panties]], and/or an adhesive backing to hold the pad in place. Reusable cloth pads are made of [[cotton]] (often [[organic farming|organic]]), [[terrycloth]], or [[flannel]], and may be handsewn (from material or reused old clothes and towels) or storebought. Disposable synthetic pads are made of [[wood pulp]] or [[synthetic]] products, usually with a [[plastic]] lining and bleached. Some sanitary napkins, particularly older styles, are held in place by a belt-like apparatus, instead of adhesive or wings. Also known simply as "pads".
+All such methods are designed to regulate monthly bleeding. Because of this, they are often chosen by females who wish to regulate the frequency and length of their period, often for basic convenience and especially when such factors are irregular and problematic on their own. Hormonal contraception has also been shown to improve menstrual factors such as cramping, heavy bleeding, and other bothersome physical and emotional issues related to periods.
-*[[Tampon]]s - Disposable wads of treated [[rayon]]/[[cotton]] blends or all-[[cotton]] fleece, usually bleached, that are inserted into the vagina to absorb menstrual flow.
-*[[Menstrual cup]]s - A firm, flexible cup- or bell-shaped device worn inside the vagina to catch menstrual flow. Reusable versions include rubber or silcone cups (like the [http://www.thekeeper.com Keeper], [http://www.divacup.com DivaCup], [http://www.lunette.fi Lunette], and [http://www.mooncup.co.uk Mooncup]). Disposable versions come in soft plastic cups (like [http://www.softcup.com/ Instead]).
-*[[Sponge|Sea sponge]]s - Natural sponges, worn internally like a tampon to absorb menstrual flow.
-*[[Padettes]] - Disposable wads of treated [[rayon]]/[[cotton]] blend fleece that are placed within the inner labia to absorb menstrual flow.
-*Padded [[Undergarment|panties]] - Reuseable cloth (usually [[cotton]]) [[undergarment|underwear]] with extra absorbent layers sewn in to absorb flow. (like [http://www.lunapads.com Lunapads])
-*[[Blanket]], [[towel]] - Large reuseable piece of cloth, most often used at night, placed between legs to absorb menstrual flow.
+===Control and flexibility===
-Pharmaceutical companies also provide products &mdash; commonly [[Non-steroidal anti-inflammatory drug]]s (NSAIDs) &mdash; to relieve menstrual cramps.
+Hormonal methods which are controlled by the user day-to-day, including pills, the ring, and the patch, need not always be used according to the standard cycle/calendar. Their use can be rescheduled and altered in various ways to postpone or skip periods when desired for reasons of convenience (e.g., traveling or scheduled gynecological exams), personal enjoyment (such as expected sexual encounters or events like a wedding or dance), or health (including very painful periods or sensitivity to hormone fluctuations). Similarly, abrupt cessation of use can induce a breakthrough period mid-cycle.
+===Other contraceptive methods===
-===Debate===
+Most [[IUD]]s are not designed to affect menstruation or breakthrough bleeding, but may exacerbate cramps or the heaviness of the flow due to their placement within the uterus. The Mirena IUD releases a small continuous dosage of a progesterone-like hormone, which can sometimes cause menstruation to cease. [[Tubal ligation|Tubal sterilization]] alone will not affect menstruation, though the [[Endometrial ablation|ablation]] option often performed at the same time will cause menstruation to cease. [[Hysterectomy]] will, of course, completely stop menstruation as it entails the removal of the [[uterus]] (and sometimes the ovaries, fallopian tubes, and cervix).  [[Fertility awareness]] methods do not affect the period in and of themselves, but involve careful observation of various kinds, of which the timing of the period is an essential factor.
-Much debate centers around which menstrual products to use. The main debate can be summarized as one between the convenience, availability, and general knowledge of disposables; versus the environmental, monetary, and potential health benefits of reuseables. A secondary aspect of this is commercial responsibility. Disposable menstrual products compose a large and powerful industry in the West, with a near monopoly on advertising, supermarket shelves, and menstrual education. This leads many people to believe that these corporate products are their only options. Many people object to the negative portrayal of menstruation in advertising; menstruation is sometimes portrayed as shameful, unnatural, smelly, and hindering. In contrast, the reuseable menstrual products industry is composed mostly of small, independent, and woman-owned businesses.{{citation needed}} Finally, some believe that the disposable menstrual products industry is imperialist, forcing or coercing women of other cultures to leave their reuseable, inexpensive or free menstrual products to become consumers of disposables.
+==Menstruation and the moon ==
-A summary of the main issues of debate:
+''See also: [[Culture and menstruation]]''
-* Environmental waste : Tampons, pads, disposable cups and their packaging generate tons of bulky waste per year, much of which is not biodegradable.
+Traditional sources agree that the menstrual cycle is linked to the cycle of the moon. These sources generally indicate that women menstruate at the time of the new moon, and ovulate at the full moon. Although scientific evidence for this has been weak, the problem may be that most women today live in urban environments where the moon is no longer a significant contributor to nocturnal light.  The fact that women who work on night shifts, where they are exposed to strong light at night, often experience menstrual irregularities, is just one example of how rhythms of light and darkness do influence hormonal physiology, including the menstrual cycle.<ref>Cohen S. "Melatonin, menstruation and the moon" ''Townsend Letter for Doctors and Patients'',  Feb-March, 2005.[http://www.findarticles.com/p/articles/mi_m0ISW/is_259-260/ai_n10299307/pg_1]</ref>
-* Cost : Many disposables have a cheaper upfront cost than reuseables, but over time (a period of a few months), this cost is recouped many times over from savings on reuseables. Many reuseables can also be made for free from old clothes or other scraps of cloth.
-* Health concerns:
-*# [[Bleaching]] - Many women object to the chlorine bleaching of disposable menstrual products, which leaves trace amounts of [[dioxin]], a [[carcinogen]], in their bodies.
-*# Scents and deodorizers - Chemical scents and deodorizers can cause rashes, irritation, and allergic reactions. They can upset the pH balance of the vagina and cause yeast infections.
-*# Specific to [[tampons]] : [[Toxic Shock Syndrome]] is indirectly caused by [[Staphylococcus aureus]], which can thrive in the environment found in tampon fibers. TSS is ''very rare'', with only approx. 40 cases per year in the [[United Kingdom|UK]]. Tampon-associated TSS is not caused by the staphylococci invading into tissues, but rather as a result of the release of a protein called [[toxic shock syndrome toxin]] (TSST).<!--
-  --><ref name="Baron">{{cite book | editor = Samule Baron | title =Medical Microbiology (Online book) | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed | accessdate = 2006-04-02 | edition = 4th edition | year = 1996 | publisher = University of Texas Medical Branch | id = ISBN 0-9631172-1-1 | chapter = Staphylococcus - Damage to Host | chapterurl = http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=toxic+shock+syndrome+AND+mmed%5Bbook%5D+AND+147524%5Buid%5D&rid=mmed.section.769#775}}</ref><!--
---> TSST is absorbed into the body where it acts as a toxin. Toxic Shock Syndrome can, and does, cause death. TSS can be avoided by using the least absorbent tampon possible for one's flow, and changing tampons at least every 8 hours, or by avoiding tampons altogether. This may apply to [[sea sponge]]s also, though no cases of TSS with sea sponge use have been reported.
+The very word menstruation is etymologically related to moon. The terms "menstruation" and "menses" come from the [[Latin]] ''mensis'' (month), which in turn relates to the [[Greek language|Greek]] ''mene'' (moon) and to the roots of the English words ''month'' and ''moon'' &mdash; reflecting the fact that the [[moon]] also takes close to 28 days to revolve around the Earth (actually 27.32 days). The synodical [[lunar month]], the period between two new moons (or full moons), is 29.53 days long.
-==Culture and menstruation ==
-{{main|Culture and menstruation}}
+A 1975 book by Louise Lacey documented the experience of herself and 27 of her friends, who found that when they removed all artificial nightlighting their menstrual cycles began to occur in rhythm with the lunar cycle. She dubbed the technique [[Lunaception]].<ref>Lacey, Louise. ''Lunaception: A Feminine Odyssey into Fertility and Contraception''. New York: Coward, McCann & Geoghegan, 1975.</ref> Later studies in both humans<ref>Singer, Katie. "[http://www.westonaprice.org/women/fertility.html Fertility Awareness,
-Many religions have menstruation-related traditions.  These may be bans on certain actions during menstruation (such as intercourse in orthodox Islam), or rituals to be performed at the end of each menses (such as the ''mikvah'' in Judaism).
+Food, and Night-Lighting]". ''Wise Traditions in Food, Farming and the Healing Arts'', Spring 2004. See section on Night-Lighting.</ref> and animals<ref>Harder, Ben. ''Bright nights kindle cancers in mice''. ''Science News'', Week of Aug. 28, 2004; Vol. 166, No. 9 , p. 141.</ref> have found that artificial light at night does influence the menstrual cycle in humans and the estrus cycle in mice (cycles are more regular in the absence of artificial light at night), though none have duplicated the synchronization of women's menstrual cycles with the lunar cycle. One author has suggested that sensitivity of women's cycles to nightlighting is caused by nutritional deficiencies of certain vitamins and minerals.<ref>Shannon, Marilyn.  ''Fertility, Cycles, and Nutrition''. Cincinnati, Ohio: The Couple to Couple League International, 2001. pp. 71–72.</ref>
+Some have suggested that the fact that [[#Menstrual cycles in other mammals|other animals' menstrual cycles]] appear to be greatly different from lunar cycles is evidence that the average length of humans' cycle is most likely a coincidence.<ref>As cited by Adams, Cecil, [http://www.straightdope.com/classics/a990924.html "What's the link between the moon and menstruation?"] (accessed [[6 June]] [[2006]]): {{cite book | last = Abell | first = George O. | authorlink = George Ogden Abell | coauthors = Barry Singer | year = 1983 | title = Science and the Paranormal: Probing the Existence of the Supernatural | publisher = Scribner Book Company | id = ISBN 0-684-17820-6}}</ref><ref>Cutler WB. Lunar and menstrual phase locking. Am J Obstet Gynecol. 1980 Aug 1;137(7):834-9. PMID: 7405975.<br />Friedmann E. Menstrual and lunar cycles. Am J Obstet Gynecol. 1981 Jun 1;140(3):350. PMID: 7246643<br /> 	Law SP. The regulation of menstrual cycle and its relationship to the moon. Acta Obstet Gynecol Scand. 1986;65(1):45-8. PMID: 3716780<br />Zimecki M. [http://www.phmd.pl/modules.php?name=Current_Issue&d_op=downloadPMID&id=8121 The lunar cycle: effects on human and animal behavior and physiology.] Postepy Hig Med Dosw (Online). 2006;60:1–7. Review.
+PMID: 16407788</ref>
+== Menstrual cycles in other mammals ==
+Females of most species advertise ovulation to males with visual cues and behavioral cues, [[pheromones]], or both (humans are a [[#Hidden ovulation|notable exception]]).  This period of advertised fertility is known as ''estrous'' or ''heat''.  However, in animals with menstrual cycles, females can be sexually active at any time in their cycle, even when they are not in heat.  Great apes' cycles vary in length from an average of 29 days in [[orangutan]]s to an average of 37 days in [[chimpanzee]]s.
+By contrast, in species that have [[estrous cycle]]s rather than menstrual cycles, females are ''only'' receptive to copulation while they are in heat ([[dolphin]]s are a notable exception). The other significant difference is that in an estrous cycle, if no fertilization takes place, the uterus reabsorbs the endometrium: no menstrual bleeding occurs.  Some animals, such as domestic [[cat]]s and [[dog]]s, experience small amounts of bleeding while in heat.  This phase of the estrous cycle corresponds most closely to the follicular phase of the menstrual cycle and should not be confused with menstruation.
-== Menstruation in other mammals ==
-A regular menstrual cycle as described here only occurs in the [[great ape]]s. Menstrual cycles vary in length from an average of 29 days in [[orangutan]]s to an average of 37 days in [[chimpanzee]]s.
+==See also==
-Females of other [[mammal|mammalian]] species go through certain episodes called "[[estrus]]" or "heat" in each breeding season. During these times, ovulation occurs and females become receptive to mating, a fact advertised to males in some way. If no fertilisation takes place, the uterus reabsorbs the endometrium: no menstrual bleeding occurs. Significant differences exist between the [[estrus]] and the menstrual cycle. Some animals, such as domestic [[cat]]s and [[dog]]s do produce a very short and mild menstrual flow. However, due to its small amount (and personal cleanliness in cats) it passes pet owners largely unnoticed.
+*[[Catamenial epilepsy]]
+*[[McClintock effect]]
+*[[Premenstrual tension]]
+*[[Premenstrual dysphoric disorder]]
 ==References==
@@ Line 164: / Line 190: @@
 </div>
-== External links ==
+==External links==
 *[http://mum.org/ Museum of Menstruation and Women's Health]
+*[http://www.cemcor.ubc.ca/ Centre for Menstrual Cycle and Ovulation Research]
-*[http://www.holyhormones.com Leslie Botha-Williams, Women's Health Educator: A Woman's Guide to Understanding Her Hormone Cycle]
-*[http://63.175.194.25/index.php?ln=eng&ds=qa&lv=browse&QR=43028&dgn=4 An Islamic answer for the ruling of women menstruating]
-*[http://www.noperiod.com Menstrual Suppression With Birth Control Pills]
-*[http://www.scarleteen.com/body/ontherag.html On The Rag: Everything you need to know about your fertility cycles and menstruation...period] - Article on the menstrual cycle by notable sex activist and educator Heather Corinna
-*[http://www.womenshealthchannel.com/menopause/menstrualcycle.shtml Menopause and Menstrual Cycles - WomensHealthChannel]
-*[http://www.ebaumsworld.com/periods101.html Early 70s Educational Film]
-'''Hygiene products'''
-*[http://www.livejournal.com/users/incendiaryfs/204904.html Love Your Blood: An info-zine on menstrual products and their alternatives]
-*[http://www.powerhousemuseum.com/rags/ The rags: paraphernalia of menstruation]
-*[http://www.scarleteen.com/pink/washable.html Eight Myths About Washable Menstrual Pads Dispelled]
-*[http://www.seac.org/tampons/ Tampaction] and [http://bloodsisters.org/bloodsisters/ The Bloodsisters Project]- Menstrual activism against chlorine bleaching, excessive packaging, and negative attitudes toward menstruation in the West
+{{Reproductive physiology}}
-{{featured article}}
+{{Menstrual cycle}}
 [[Category:Female reproductive system]]
 [[Category:Gynecology]]
-[[Category:Menstruation]]
+[[Category:Menstrual cycle]]
+[[Category:Menstruation| ]]
+<!--
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+[[bs:Menstrualni ciklus]]
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+[[fa:عادت ماهانه]]
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+[[fr:Cycle menstruel]]
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@@ Line 201: / Line 222: @@
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+[[pt:Ciclo menstrual]]
 [[ru:Менструальный цикл]]
 [[sr:Менструација]]
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+[[ta:மாதவிடாய்]]
 [[vi:Chu kỳ kinh nguyệt]]
+[[uk:Менструальний цикл]]
 [[zh:月經]]
+-->
 {{enWP| Menstrual cycle}}