Amniocentesis: Why It Is Done

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Why It Is Done

Amniocentesis may be done during your second trimester of pregnancy (between weeks 15 and 20) to find some birth defects. Amniocentesis may be done when:

• You would like to have a test that will tell you for sure if your baby has Down syndrome or another chromosome problem.
• Either you or the father has a family history of birth defects.
• Both you and the father are known carriers of a family disease, such as Tay-Sachs disease, sickle cell anemia, thalassemia (Mediterranean anemia), or cystic fibrosis.
• You had a screening test done in the first trimester that showed your baby has a higher chance of a birth defect.
• You had an integrated test that showed your baby has a higher chance of a birth defect. This test is a combination of several tests done in two stages at two different times during the pregnancy. A positive result may mean Down syndrome is present.
• You had a triple or quadruple screen test that showed your baby has a higher chance of a birth defect. The substances measured in a triple test are alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and estriol. An additional substance, the hormone inhibin A, is measured in the quadruple test.

Amniocentesis can tell the sex of your fetus. This is important when you or the father may be able to pass on a disease that occurs mainly in one sex (sex-linked), such as hemophilia or Duchenne muscular dystrophy, both of which occur mainly in males.

Amniocentesis may be done during your third trimester to:

• See if your fetus's lungs are mature. This may be done when you may need to deliver early because of a problem with the pregnancy.
• See whether the amniotic fluid is infected (chorioamnionitis).

Last updated:	May 14, 2008
Author:	Sandy Jocoy, RN
Reviewed By:	Sarah Marshall, MD - Family Medicine, Siobhan M. Dolan, MD, MPH - Reproductive Genetics
Editors:	Kathleen M. Ariss, MS, Tracy Landauer