What is amniocentesis?

During pregnancy, the fetus is surrounded by amniotic fluid, a substance similar to water that contains fetal cells which are shed during development. These cells can be used to provide genetic and other important information about the health of the fetus before birth.

Amniocentesis is a procedure in which a small amount of amniotic fluid from the sac surrounding the fetus is removed and tested. The sample of amniotic fluid (less than 1 ounce) is removed with a fine needle inserted into the uterus through the abdomen, under ultrasound guidance.

The fluid is then sent to a laboratory for analysis. Different tests can be performed on a sample of amniotic fluid, depending on what the underlying concern is.

Why is an amniocentesis performed?

Amniocentesis is often performed to determine if the fetus is affected with a genetic condition, such as Down syndrome (a chromosomal abnormality). Because genetic amniocentesis presents a small risk for both the mother and her baby, it is generally offered only to women who have a significant risk for genetic disorders. These can include women with:

  • Fetal abnormalities noted on an ultrasound
  • A positive screening test for a chromosome abnormality
  • A family history or have previously had a child with a genetic disorder

It may also be offered to mothers who will be 35 or older at the time of delivery.

Amniocentesis can also be used to detect certain diseases, which are caused by abnormalities in a single gene. It may be used if there is risk for that disease in the fetus based on either family history or carrier screening testing in the parent(s). Some diseases include:

  • Sickle cell disease
  • Cystic fibrosis
  • Tay-Sachs disease
  • Muscular dystrophy

When is amniocentesis performed?

If your doctor has recommended an amniocentesis, the procedure can be performed any time after the 15th week of pregnancy. Most are done before 20 weeks of pregnancy.

Can I choose not to have an amniocentesis?

Yes. You will receive genetic counseling before the procedure. After the risks and benefits of amniocentesis have been thoroughly explained, you can choose whether or not you want to have the procedure.