Handbook of Genetic Counseling/Advanced Maternal Age - Amniocentesis

Advanced Maternal Age - Amniocentesis

Introduction

• 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 Intake

• 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?

• 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?

• 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 Assessment

• 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?

• 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

Ultrasound

• 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.

Amniocentesis

• 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 Procedure

• 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 Amnio

• 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 Amnio

• 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 Amnio

• 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).

Conclusion

• 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.

Notes

The information in this outline was last updated in 2001.