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Genetic counseling: Advanced Maternal Age - Amniocentesis

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Advanced Maternal Age - Amniocentesis

IntroductionEdit

  • Welcome and acknowledge any prior phone contact.
  • Discuss the reason for referral. Do they understand why they were sent to genetics?
  • Assess their concerns and what they hope to gain from the session.
  • Assess their degree of knowledge about genetics, heredity, AMA, etc.
  • Provide overview of the session and discussion topics.

Prenatal IntakeEdit

  • Obtain client and partner information (age, occupation, ethnicity, religion, consanguinity, health)
  • Elicit family history and construct pedigree.
  • Pregnancy history (dates, procedures, exposures, complications)
  • Discuss population pregnancy information - every pregnancy has a 3-5% risk for congenital malformations; every pregnancy has a 2-3% risk of miscarriage.

What is AMA?Edit

  • Advanced maternal age applies to anyone aged 35 years or above at the expected date of delivery.
  • As maternal age increases, the risk of birth defects (particularly chromosomal abnormalities) increases.
  • Age 35 is the cutoff for AMA because this is the point where the procedural risk equals the risk of aneuploidy.

What are chromosomal abnormalities?Edit

  • Explanation of chromosomes.
  • Explanation of meiosis, haploid germ cells, fertilization to a diploid zygote.
  • Explanation of non-disjunction. Focus on how women are born with all their eggs and they mature with age.
  • Discuss common trisomies/monosomies (13, 18, 21, 47XXY, 45X), show karotypes, and give general description of clinical features and prognoses.

Risk AssessmentEdit

  • Discuss client's age-related mid-trimester risks for any chromosomal abnormalities and for Down syndrome in particular.
  • Record data on intake.

What are the testing options?Edit

  • Triple Marker Screening:
    • Maternal blood test performed at 15-22 weeks.
    • Screening test only, NOT diagnostic.
    • Indirect measurement of fetal AFP, hCG, uE3 production.
    • Detects approx. 85% NTDs, up to 85-90% of DS, and up to 80% of Trisomy 18 in women with AMA.
    • False-positive rate of 25% in women over 35 years of age.
    • Does not detect all chromosomal abnormalities assoc. with AMA

UltrasoundEdit

  • Can detect many major birth defects.
  • Some fetuses with chromosomal abnormalities have characteristics that can be seen by ultrasound as "markers", but others have no visible anomalies.
  • Ultrasound can NOT diagnose chromosome abnormalities.

AmniocentesisEdit

  • Medical procedure that removes a small sample of amniotic fluid (made of fetal urine, contains fetal skin cells) from the amniotic sac surrounding the fetus.
  • Usually performed between 15-18 weeks (although some labs will interpret data from 13.5 to 21 weeks)
  • Fluid is used for genetic analysis - fetal karyotyping, biochemical studies, DNA studies, alpha-fetoprotein and acetyl cholinesterase measurements.

Amnio ProcedureEdit

  • Procedure takes 20-45 minutes (1-2 minutes for needle insertion).
  • May be required to have a full bladder.
  • Lie down on back with hands folded behind your head.
  • Abdomen cleansed with betadeine.
  • Local anesthetic (xylocaine) may be used to numb the outer layer of skin - this may feel like a pin prick followed by a stinging or burning sensation.
  • Ultrasound is used to locate the fetus and placenta, identify the pocket of fluid, and guide the needle.
  • Physician inserts the needle (22 gauge with a stylet) through the abdomen and into the uterus - some discomfort may be felt when the needle enters the skin and then the uterus (may feel like a menstrual cramp); a sharp pain lasting a few seconds may be felt when the needle enters the amniotic sac.
  • Stylet is removed and the first few cc of fluid are discarded due to possible maternal cell contamination. About 20 cc (1 tablespoon) of amniotic fluid is removed - may feel pressure in the lower abdomen when the fluid is withdrawn; is quickly replaced by the fetus.
  • Needle is removed, bandage applied, fetal heart activity is monitored by ultrasound, no overnight hospital stay.
  • Fluid is sent to lab and results are available in 1-2 weeks. Discuss how results will be received.
  • About 95% of women receive a negative result.
  • Total cost is $600-$900.
  • Afterwards, no strenuous activity for 24 hours. Follow up with MSAFP at 16-18 weeks and ultrasound at 18-20 weeks.

Benefits of AmnioEdit

  • Accuracy of karyotype is >99% (NTD detection is about 90-96%).
  • Can detect chromosomal abnormalities (aneuploidies).
  • Can detect neural tube defects (spina bifida, anencephaly).
  • Tells the sex of the fetus.

Limitations of AmnioEdit

  • Does not detect all possible birth defects (only about 10% of 400 known congenital malformations).
  • Cannot predict the severity of the defect/disorder.
  • If first procedure fails, a second may be attempted that same day. If it doesn't work, then additional procedures should be postponed for 3-7 days.
  • Cell culture failure could occur (rare, <1%).

Risks Associated with AmnioEdit

  • Risk of miscarriage - 1/200 (0.5% beyond background risk).
  • Rh (-) mothers must be given RhoGam in order to prevent blood group sensitization.
  • Uterine cramping is not uncommon.
  • Notify your doctor is you have transient spotting or leakage of amniotic fluid (2-3% of cases).
  • Very rare chance of infection to uterus, hemorrhage, or maternal death.
  • Risk of birth defects due to amnio is remote (risk of clubfoot increased during early amnio).

ConclusionEdit

  • Discuss psychosocial issues that may arise.
  • Remind that no decision has to be made today.
  • Review and summarize.
  • Answer final questions and concerns.
  • Give out patient resources.

NotesEdit

The information in this outline was last updated in 2001.


Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling

Heckert GNU white Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License."

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