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Harvard Medical School
Amniocentesis involves using a needle to take a sample of amniotic fluid, the fluid that surrounds a developing fetus during pregnancy. Tests of fetal cells found in this fluid can reveal the presence of Down syndrome or other chromosome problems in the baby. Amniocentesis can also show whether the lungs of the baby are mature enough to allow it to survive if it were delivered right away.
Amniocentesis is often recommended for pregnant women over age 35, women who have an abnormal "triple screen" blood test during pregnancy, or women who have (or whose husbands have) a family history of certain diseases or birth defects.
A different test that provides similar information is called chorionic villus sampling (CVS). Women can have CVS done slightly earlier in pregnancy. Your doctor can help you to decide which test is most appropriate for you.