What is amniocentesis?

Amniocentesis is a test performed during pregnancy to diagnose genetic disorders, chromosomal abnormalities, and birth defects. It can also help diagnose certain infections and the maturity of your baby’s lungs. 

Amniocentesis involves inserting a needle through the abdomen to take out a small amount of amniotic fluid from inside the uterus. Amniotic fluid is the liquid that surrounds the growing fetus. The amniotic fluid sample is tested in a laboratory. 

An amniocentesis is only one method used to test for conditions of a fetus. You may have less invasive testing options. Discuss all of your testing options with your doctor or healthcare provider to understand which options are right for you.

Why is amniocentesis performed? 

Your doctor may recommend an amniocentesis to diagnose certain diseases and conditions of the fetus including:

  • Anencephaly, a serious birth defect in which a large part of the brain and skull are not formed
  • Cystic fibrosis, a genetic disease in which the body makes too much mucus and sweat
  • Down syndrome and other conditions caused by chromosomal abnormalities
  • Infections of the uterus or the baby
  • Need for early delivery. Your doctor may perform an amniocentesis when considering inducing early labor. Early labor and delivery protects the health of the mother or baby in some cases. Testing the amniotic fluid helps determine if the baby’s lungs are developed enough for birth.
  • Rh incompatibility of the mother and baby. This is a condition in which the mother has Rh-negative blood and her baby has Rh-positive blood. This can cause a reaction that breaks down the infant’s red blood cells. The reaction can be mild to serious and cause yellow skin and eyes (jaundice), lethargy, and low muscle tone.
  • Spina bifida and other serious neural tube defects caused by incomplete closure of the spine during fetal development 

Doctors also perform amniocentesis to drain extra amniotic fluid in rare cases. Too much amniotic fluid (polyhydramnios) increases the risk of premature labor and delivery and other serious problems.

Ask your doctor about all of your testing and treatment options and consider getting a second opinion before deciding on amniocentesis. 

Who performs amniocentesis?

An obstetrician-gynecologist or perinatologist performs amniocentesis. An obstetrician-gynecologist specializes in the health needs of adolescent and adult women, including pregnancy and labor and delivery. A perinatologist, also called a maternal-fetal medicine specialist, is a doctor who specializes in high-risk pregnancies.

How is amniocentesis performed?

Amniocentesis is most often performed between 15 and 20 weeks of pregnancy (during the second trimester). It is performed later to test for infection and your baby’s lung development.

Your amniocentesis will be performed in a doctor’s office or outpatient hospital clinic. It takes about an hour and generally includes these steps:

  1. You dress in a patient gown from the waist up. 
  2. You lie on your back on a procedure table. Your doctor may move or tilt the table during your exam.
  3. Your doctor puts ultrasound gel on your abdomen. The gel helps the ultrasound equipment make full contact with your skin by eliminating air. It also allows the equipment to slide easily across your skin without discomfort.
  4. Your doctor places an ultrasound transducer on your skin. The transducer is a handheld wand that sends and receives sound waves. The doctor presses it firmly onto your skin and moves it around to see your uterus and fetus. The transducer and sound waves are painless.
  5. Your doctor uses the ultrasound images to guide needle insertion. Your doctor will push the needle through your abdomen until it enters the uterus.
  6. Your doctor removes about an ounce of amniotic fluid and withdraws the needle. 
  7. Your doctor may perform more ultrasound imaging see how the fetus is developing.
  8. Your doctor wipes off the gel. The gel is water-based and washes away easily.
  9. You may wait a short period while your doctor verifies that the ultrasound imaging is complete. Women usually go home right after the exam.
  10. A laboratory tests your amniotic fluid. You will get the results in about two weeks.