Amniocentesis

What is amniocentesis?

Amniocentesis is a procedure used to test for birth defects. It involves obtaining a sample of amniotic fluid (fluid in the amniotic sac that surrounds the fetus) from which cells of the fetus can be tested. It can detect chromosomal problems such as Down syndrome , or genetic diseases such as cystic fibrosis , Tay-Sach's disease , and sickle cell disease . It can also detect the sex of the fetus.

Who should have amniocentesis?

Your health care provider will make recommendations for testing based on your genetic risk. Testing should be recommended if:

• You will be 35 years old or older when you give birth.
• You have a family history of certain birth defects.
• You already had a child with a birth defect.
• You have abnormal results on other genetic tests.

How is the procedure performed?

Amniocentesis is usually done in the 15th to 18th week of pregnancy. The procedure is performed in the health care provider's office or hospital and does not require an overnight stay. You will lay down with your abdomen uncovered. You will then be given an ultrasound. The ultrasound helps the clinician will know where to insert the needle that will be used to withdraw the sample of amniotic fluid. The needle will then be carefully placed through the your abdomen and uterus and into the amniotic sac. If you are carrying twins, you will need to have fluid withdrawn from each amniotic sac. About 1 ounce of fluid is withdrawn and then sent to the lab so that the cells can be tested. Results may take about two weeks.

Other tests for birth defects can be performed using the amniotic fluid, including the alpha-fetoprotein (AFP) test . AFP is a protein produced by the fetus, which passes into the amniotic fluid. Too much AFP can be a sign of open neural tube defects or openings in the abdomen of the fetus. AFP can also be checked with a blood test.

Are there any risks associated with amniocentesis?

Amniocentesis tends to be a fairly safe procedure for the mother and her fetus. However, complications occur in a minority of cases and may include:

• Cramping, bleeding, or infection
• Leaking of amniotic fluid
• Miscarriage (in less than 1 out of every 200 women who have the test)