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Amniocentesis

What is amniocentesis?

Amniocentesis is a prenatal diagnostic procedure that is performed between 16-20 weeks of pregnancy. Amniotic fluid, which is the fluid that surrounds the fetus, contains cells that have naturally shed off of the fetus. During the procedure, a small amount of amniotic fluid is removed. The cells within the fluid can then be evaluated in a lab to test for chromosome and/or specific genetic disorders. A protein called Alpha-fetoprotein (AFP) is also found in the fluid. AFP can be measured to determine whether the fetus is at increased risk for specific birth defects.

Who should consider amniocentesis?

Previous recommendations stated that women who are 35 years or older at the time of delivery should consider amniocentesis. However, in 2007 the American College of Obstetricians and Gynecologists (ACOG) released new recommendations stating the following.

• All women regardless of age should have the option of diagnostic testing, such as amniocentesis

Additionally, amniocentesis should be considered for the following:

• Women with an increased risk for a chromosome abnormality found on a screening test (for example: Combined First Trimester screening, Integrated screening, Expanded AFP etc.).
• Couples in which one partner carries a chromosome rearrangement, such as a translocation.
• Couples with a family history of a chromosome abnormality.
• Couples at increased risk of having a child with a testable genetic disease (for example: Cystic Fibrosis, Tay Sachs Disease, etc.).

How is amniocentesis performed?

Patients will meet with a genetic counselor before the procedure to obtain a thorough genetic history. A fetal survey is performed to screen for birth defects, check dates of the pregnancy, and to evaluate the placenta as well as amniotic fluid levels. Under ultrasound guidance, a specially trained perinatologist inserts a thin needle into the maternal abdomen and the uterus to remove a small amount of the fluid surrounding the fetus. The fluid is then sent to the lab for chromosome and protein analysis.

What can be detected by amniocentesis?

• Chromosome abnormalities such as Down syndrome.
• Specific known genetic conditions in a family, such as cystic fibrosis (CF).
• Abnormal levels of proteins in the amniotic fluid that might signal a specific birth defect such as neural tube defects (i.e. spina bifida).

It is important to remember that although amniocentesis is considered diagnostic, results cannot detect all birth defects, genetic conditions, or types of mental retardation.

What preparations are necessary before the procedure?

Women should refrain from taking aspirin or aspirin-containing products for 5 days before the procedure. Heparin should also be discontinued for 24 hours before the procedure.

What are the recommendations after the procedure?

After the procedure, it is important go home and rest for the remainder of the day.

Additionally, we suggest:

• No lifting over 15 pounds for 24 hours.
• No exercise, intercourse, or travel by plane for 48 hours (2 days).

What are the risks?

Recent studies have suggested that the procedure–related loss rate is as low as 1 in 300-500 and may be even lower with experienced individuals or centers. Additionally, the majority of women experience little to no complications after amniocentesis. Minor complications might include a small amount of fluid leakage, spotting or light bleeding, and/or cramping.

When are results available?

Chromosome and AFP results are typically ready about 10 to 12 days after the procedure. Studies which look for specific genetic conditions may take longer.

To schedule amniocentesis, please contact San Francisco Perinatal Associates at 415-202-1200. Should you have additional questions about amniocentesis, please feel free to call and speak with a genetic counselor.