Amniocentesis is a diagnostic procedure that is used before birth to look for genetic problems and birth defects in the developing fetus. During the procedure, your doctor removes a small amount of amniotic fluid from the uterus using a long needle. In addition to protecting and surrounding the baby while in the womb, amniotic fluid also promotes the development of your baby’s lungs, digestive system, muscles and bones. It also contains chemicals that the baby produces and fetal cells.

The test is usually performed during the second trimester, typically between 15 and 20 weeks of pregnancy. Your doctor may also choose to perform an amniocentesis during your third trimester to check for possible infections in the uterus or to ensure that your baby’s lungs have developed sufficiently for an early birth. Not all expectant mothers require an amniocentesis, and because there is some risk with the procedure, doctors only prescribe them if there is a sufficient reason.

How is the test performed?

Amniocentesis can be completed in 15-20 minutes. For the first part of the procedure, you will receive an ultrasound to determine the location of your baby within the uterus. The ultrasound will also help your healthcare provider locate the placenta and the pockets of amniotic fluid.

With the guidance of ultrasound, your doctor will place a thin needle through your stomach and uterus and into the amniotic sac. The needle removes approximately one ounce of fluid, which will be sent to a laboratory for testing. Afterward, your healthcare provider will use ultrasound to examine your baby’s heartbeat.


After separating your baby’s cells from the amniotic fluid, they are cultured and analyzed to check for potential problems. Depending on the tests being performed, results are typically available within a two-week period. After this period of time, a genetic counselor or your healthcare provider will discuss the results of your amniocentesis.


  • An amniocentesis is a prenatal test that diagnoses genetic conditions and birth defects.
  • A sample of amniotic fluid is removed during the procedure.
  • The procedure is commonly performed during the second trimester.
  • Results from an amniocentesis are usually available within two weeks. 

Last reviewed by Jennifer Lincoln, MD, IBCLC. Review Date: August 2019


  1. March of Dimes. Pregnancy complications.
  2. March of Dimes. Prenatal care.
  3. Mayo Clinic. Amniocentesis.


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