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Fertility is the natural capability of giving life. As a measure, "fertility rate" is the number of children born per couple, person or population. This is different from fecundity, which is defined as the potential for reproduction (influenced by gamete production, fertilisation and carrying a pregnancy to term). Infertility is a deficient fertility.

Human fertility depends on factors of nutrition, sexual behavior, culture, instinct, emotions.endocrinology, economics, life style, stress and timing,


DemographyEdit

In demographic contexts, fertility refers the actual production of offspring, rather than the physical capability to produce which is termed fecundity.[1][2] While fertility can be measured, fecundity cannot be. Demographers measure the fertility rate in a variety of ways. One such indicator, the total fertility rate, is the number of children a woman would bear during her lifetime if she were to experience the prevailing age-specific fertility rates of women. Another commonly-used indicator, the crude birth rate, is the number of children born alive in a given year per 1,000 people alive at the middle of that year. One disadvantage of this indicator is that it is influenced by the age structure of the population.

Human fertilityEdit

Both women and men have hormonal cycles which determine both when a woman can achieve pregnancy and when a man is most virile. The female cycle is approximately twenty-eight days long, but the male cycle is variable. Men can ejaculate and produce sperm at any time of the month, but their sperm quality dips occasionally, which scientists guess is in relation to their internal cycle.

Furthermore, age also plays a role, especially for women.

Menstrual cycleEdit

Main article: Menstrual cycle

Although women can become pregnant at any time during their menstrual cycle, peak fertility occurs during just a few days of the cycle: usually two days before and two days after the ovulation date[3]. This fertile window, varies from woman to woman, just as the ovulation date often varies from cycle to cycle for the same woman[4]. The ovule is usually capable of being fertilized for up to 48 hours after it is released from the ovary. Sperm survive inside the uterus between 48 to 72 hours on average, with the maximum being 120 hours (5 days).

These periods and intervals are important factors for couples using the rhythm method of contraception.

Female fertilityEdit

The average age of menarche in the United States is about 12.5 years.[5] In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year.[6][7] Women's fertility peaks around the age of 19-24, and often declines after 30.[How to reference and link to summary or text] With a rise in women postponing pregnancy,[8] this can create an infertility problem. Of women trying to get pregnant, without using fertility drugs or in vitro fertilization:

  • At age 30, 75% will get pregnant within one year, and 91% within four years.
  • At age 35, 66% will get pregnant within one year, and 84% within four years.
  • At age 40, 44% will get pregnant within one year, and 64% within four years.[9]

The above figures are for pregnancies ending in a live birth and take into account the increasing rates of miscarriage in the aging population. According to the March of Dimes, "about 9 percent of recognised pregnancies for women aged 20 to 24 ended in miscarriage. The risk rose to about 20 percent at age 35 to 39, and more than 50 percent by age 42".[10]

Birth defects, especially those involving chromosome number and arrangement, also increase with the age of the mother. According to the March of Dimes, "At age 25, a woman has about a 1-in-1,250 chance of having a baby with Down syndrome; at age 30, a 1-in-1,000 chance; at age 35, a 1-in-400 chance; at age 40, a 1-in-100 chance; and at 45, a 1-in-30 chance."[11]

The use of fertility drugs and/or invitro fertilization can increase the chances of becoming pregnant at a later age. Successful pregnancies facilitated by fertility treatment have been documented in women as old as 67.[12]

Doctors recommend that women over 30 who have been unsuccessful in trying to conceive for more than 6 months undergo some kind of fertility testing.[13]

Male fertility and ageEdit

Erectile dysfunction increases with age,[14] but fertility does not decline in men as sharply as it does in women. There have been examples of males being fertile at 94 years old.[14] However, evidence suggests that increased male age is associated with a decline in semen volume, sperm motility, and sperm morphology.[15] In studies that controlled for female age, comparisons between men under 30 and men over 50 found relative decreases in pregnancy rates between 23% and 38%.[15]

Cause of declineEdit

Sperm count declines with age, with men aged 50-80 years producing sperm at an average rate of 75% compared with men aged 20-50 years. However, an even larger difference is seen in how many of the seminiferous tubules in the testes contain mature sperm;

  • In males 20-39 years old, 90% of the seminiferous tubules contain mature sperm.
  • In males 40-69 years old, 50% of the seminiferous tubules contain mature sperm.
  • In males 80 years old and older, 10% of the seminiferous tubules contain mature sperm.[14]

Recent research has suggested increased risks for health problems for children of older fathers. A large scale Israeli study found that the children of men 40 or older were 5.75 times more likely than children of men under 30 to have an autism spectrum disorder, controlling for year of birth, socioeconomic status, and maternal age.[16] Increased paternal age has also been correlated to schizophrenia in numerous studies.[17][18][19]

The American Fertility Society recommends an age limit for sperm donors of 50 years or less,[20] and many fertility clinics in the United Kingdom will not accept donations from men over 40 or 45 years of age. [21] In part because of this fact, more women are now using a take-home baby rate calculator to estimate their chances of success following invitro fertilization. [22]

InfertilityEdit

see also Infertility

See alsoEdit

ReferencesEdit

  1. http://www.gfmer.ch/Books/Reproductive_health/The_demography_of_fertility_and_infertility.html
  2. http://www.enotes.com/public-health-encyclopedia/fecundity-fertility
  3. http://www.duofertility.com/en/my-body/my-cycle/my-fertile-period.html
  4. Creinin MD, Keverline S, Meyn LA (October 2004). How regular is regular? An analysis of menstrual cycle regularity. Contraception 70 (4): 289–92.
  5. Anderson SE, Dallal GE, Must A (April 2003). Relative weight and race influence average age at menarche: results from two nationally representative surveys of US girls studied 25 years apart. Pediatrics 111 (4 Pt 1): 844–50.
  6. Apter D (February 1980). Serum steroids and pituitary hormones in female puberty: a partly longitudinal study. Clin. Endocrinol. (Oxf) 12 (2): 107–20.
  7. Apter D (February 1980). Serum steroids and pituitary hormones in female puberty: a partly longitudinal study. Clin. Endocrinol. (Oxf) 12 (2): 107–20.
  8. http://findarticles.com/p/articles/mi_m1077/is_1_62/ai_n16807720 "Late-in-life Pregnancy"
  9. Fertility Treatment Less Successful After 35. WebMD. URL accessed on July 4 2006.
  10. Pregnancy After 35. March of Dimes. URL accessed on May 21 2008.
  11. The sterility tax can be reestablished in Russia. URL accessed on September 22 2006.
  12. Spanish woman ' is oldest mother'. BBC News. URL accessed on 2006-12-30.
  13. Female Fertility Testing
  14. 14.0 14.1 14.2 Effect of Age on Male Fertility Seminars in Reproductive Endocrinology. Volume, Number 3, August 1991. Sherman J. Silber, M.D.
  15. 15.0 15.1 Kidd SA, Eskenazi B, Wyrobek AJ (February 2001). Effects of male age on semen quality and fertility: a review of the literature. Fertil. Steril. 75 (2): 237–48.
  16. Reichenberg A, Gross R, Weiser M, et al. (September 2006). Advancing paternal age and autism. Arch. Gen. Psychiatry 63 (9): 1026–32.
  17. Malaspina D, Harlap S, Fennig S, et al. (April 2001). Advancing paternal age and the risk of schizophrenia. Arch. Gen. Psychiatry 58 (4): 361–7.
  18. Sipos A, Rasmussen F, Harrison G, et al. (November 2004). Paternal age and schizophrenia: a population based cohort study. BMJ 329 (7474): 1070.
  19. Malaspina D, Corcoran C, Fahim C, et al. (April 2002). Paternal age and sporadic schizophrenia: evidence for de novo mutations. Am. J. Med. Genet. 114 (3): 299–303.
  20. Plas E, Berger P, Hermann M, Pflüger H (August 2000). Effects of aging on male fertility?. Exp. Gerontol. 35 (5): 543–51.
  21. Age Limit of Sperm Donors in the United Kingdom Pdf file
  22. http://www.formyodds.com

Further readingEdit

  • Jones C (March 2008). Ethical and legal conundrums of postmodern procreation. Int J Gynaecol Obstet 100 (3): 208–10.


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