Skip Navigation
Search Menu
Gynecology & Obstetrics

In This Section      
Print This Page


Amniocentesis is a procedure performed to obtain genetic information about a developing fetus by collecting a sample of amniotic fluid, the fluid that cushions a baby in utero. Women usually undergo genetic counseling before having amniocentesis.

This fluid contains cells which, when studied in a laboratory, can tell physicians if certain genetic conditions are present in the baby. Your doctor may recommend an amniocentesis because of advanced maternal age (e.g. 35 or older) or because other prenatal screenings may have revealed a risk that the baby has an inherited or congenital condition.

What are the risks to my baby?

Any diagnostic procedure carries some risk. Your physicians and the genetic counselors at the Prenatal Diagnosis and Treatment Center at Johns Hopkins will explain the test and risks so you can make an informed decision about whether to proceed.

When is this test performed?

This procedure is usually performed in the second trimester of pregnancy (starting at about 15 week’s gestation).

How is the test performed?

  1. Using ultrasound guidance, a thin needle is placed into the maternal abdomen and positioned within the amniotic fluid surrounding the fetus.
  2. A sample of amniotic fluid is obtained which can then be sent for genetic testing.
  3. Amniocentesis can also be used to test the amniotic fluid for signs of fetal infection.
  4. Amniocentesis can be performed in the late third trimester of pregnancy to evaluate fetal lung maturity.

Will I need to have a full bladder?

No, but sometimes a partially full bladder makes it easier to do the test, so we may advise you to not empty your bladder during your visit.

When will I get the results?

10-14 days, in most cases.