Amniocentesis may be done during your second trimester of pregnancy to find certain birth defects.

You may choose to have this test because:

• Of your age. As you get older, you have a greater chance of having a baby with a birth defect. Many doctors use 35 and older as the age for higher risk.
• You want to know for sure if your baby has a certain health problem. This may help you decide early whether you want to continue your pregnancy or make plans to care for a sick child.
• You or the baby's father carries an abnormal gene that is known to cause a disease, such as Tay-Sachs disease, sickle cell anemia, or cystic fibrosis.
• You or the baby's father has a family history of a genetic disorder or birth defect.
• Screening tests suggest that your chance of having a baby with a genetic disorder or birth defect is higher than average.

Amniocentesis can tell the gender of your fetus. This is important when you or the father may be able to pass on a disease that occurs mainly in one gender (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).