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.

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.

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.

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.

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

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.

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.

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.

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%).

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).

The information in this outline was last updated in 2001.

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