Amniocentesis

What is an amniocentesis?

Amniocentesis is a procedure performed by a doctor to obtain a small sample of the amniotic fluid surrounding the fetus. Floating in this fluid are fetal cells, which have sloughed off the fetus. From these cells, we are able to analyze the chromosomes and a protein in the fluid called alpha-fetoprotein (AFP), without actually touching the baby.

Before the procedure, the doctor performs an ultrasound scan (sonogram) which shows a picture of the uterus, the placenta, the amniotic fluid and the fetus on a screen. The ultrasound determines the size and the position of the fetus and the location of the placenta. This information guides the doctor as she/he decides where to place the needle for the amniocentesis.

Under ultrasound guidance, the doctor inserts a very thin needle through the woman’s abdomen into the uterus, and withdraws a small sample of amniotic fluid. This part of the procedure lasts only 1-2 minutes. The fetus quickly replaces the lost fluid within 48 hours.

Some women describe the amniocentesis procedure as similar to that of a needle prick felt in a blood draw and then feel pressure or a cramp. Other women do not experience any discomfort.

Tubes containing the sample of the amniotic fluid are closed tightly, labeled carefully and sent to a laboratory for testing. Many people find that the period of waiting for the test results is the hardest part.

Who should consider an amniocentesis?

When a pregnancy is at an increased risk for a chromosome abnormality, inherited genetic diseases, neural tube defects or other conditions for which tests are available, a woman has the option of pursuing an amniocentesis for more information.

Deciding to have an amniocentesis is a personal decision based on your special risk and concerns. A genetic counselor can help to answer any further questions you may have.

How safe is amniocentesis?

Millions of women have had prenatal diagnosis by amniocentesis. When an amniocentesis is performed under ultrasound guidance, the risk that the procedure will harm the mother or the fetus is so small that is it is almost immeasurable.

However, amniocentesis does pose a slight risk of miscarriage. The national average risk for is about 1 in 200 (0.5%). An amniocentesis performed before 15 weeks of pregnancy has a somewhat higher risk, up to about 1 in 100 (1%).

Learn more

Genetic Counseling Services translates scientific knowledge into practical information that you can use in making family decisions. For more information about genetic counseling, click here or call 918-293-6200.

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