What is an amniocentesis test?

Amniocentesis is a prenatal testing procedure usually performed during the second or third trimester of pregnancy. During amniocentesis, your provider uses a thin needle to remove a small amount of amniotic fluid from the sac surrounding your unborn baby.

This fluid sample then gets tested in a laboratory. Amniocentesis can diagnose certain genetic conditions (such as Down syndrome). It also flags other potential issues that could affect your baby’s health.

What is amniotic fluid?

During pregnancy, an unborn baby grows and develops inside the amniotic sac. Some people call the amniotic sac the “bag of waters.” Amniotic fluid surrounds and protects your baby inside the amniotic sac.

Amniotic fluid looks a lot like water. This fluid also contains some of your baby’s cells. Babies shed these cells as they grow. These cells provide genetic information and other details that can offer clues about your baby’s health before birth.

Who gets an amniocentesis test?

Your provider may recommend amniocentesis during pregnancy when:

  • Ultrasound testing detects a fetal abnormality.
  • A prenatal screening test detects an increased risk for a chromosome abnormality.
  • Certain genetic disorders (such as sickle cell disease or cystic fibrosis) run in your family.
  • Moms-to-be are 35 or older at the time of delivery. A mother of higher age increases the overall risk your baby could have a genetic disorder.

What can an amniocentesis test detect?

An amniocentesis test can detect:

This test can also evaluate:

  • Your baby’s lung development, should you need to give birth sooner than expected to protect the health of you or your baby.
  • Other health concerns, such as Rh disease, a potentially serious condition where you and your baby have different blood types.

In some cases, an amniocentesis acts as a treatment, such as for polyhydramnios. Providers may perform this procedure to remove extra amniotic fluid. Having too much amniotic fluid may affect your baby’s growth.

When is amniocentesis performed?

Most amniocentesis procedures happen between 15 and 20 weeks gestation (during the second trimester of pregnancy). Having an amniocentesis earlier in pregnancy poses more risks, such as miscarriage.

In some cases, providers perform amniocentesis tests later in pregnancy. If your provider recommends this test to check your baby’s lung development or treat polyhydramnios, it will likely happen during the third trimester.

Can I choose not to have an amniocentesis?

Yes. If your provider recommends you have an amniocentesis, they will explain why. Your provider (or a genetic counselor) will go over the test’s potential benefits and risks. In the end, whether or not to have this test is up to you.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy