Amniocentesis (also called amnio) is a common prenatal test used to diagnose certain birth defects and genetic conditions. Genetic conditions are health conditions and birth defects that are passed down to a baby from mom and dad. They may cause health problems for a baby.

Amnio is different from another prenatal test called chorionic villus sampling (CVS). Talk to your health care provider about having an amnio, CVS or other prenatal tests.

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women should have the option of having prenatal tests like amniocentesis. Your provider may recommend you have an amnio if you are at risk for having a baby with a birth defect. Most women who have an amnio find out their baby is fine.

During an amnio, your health care provider takes a small sample of amniotic fluid. Amniotic fluid is fluid that surrounds your baby in the womb. The sample is used to check your baby’s health.

It’s best to have an amnio in the second trimester between 15 and 20 weeks of pregnancy. Amniocentesis before 15 weeks is no longer recommended because it has a higher risk of miscarriage and other complications. A third-trimester amniocentesis can find infections in your uterus (womb) or check to see if your baby’s lungs are developed enough for early birth.

What are some reasons for having an amnio?

Your provider should offer you an amnio, and you can ask to have one. You may want to have an amnio if you’re at risk for having a baby with a birth defect. These risks include:

  • Being 35 or older. The risk of having a baby with certain birth defects, such as Down syndrome, increases as you get older.
  • Having a previous child or pregnancy with a birth defect. If you had a child or a pregnancy with a birth defect in the past, your provider should offer you testing.
  • Abnormal screening test results. A screening test is usually a blood test that checks to see if you or your baby is more likely than others to have a certain health condition. It's different from a diagnostic test that tells you if you do or do not have a certain health condition. If you have abnormal results from a screening test, your provider should offer you amniocentesis. Most babies with abnormal screening test results are born healthy.
  • Family history of a genetic condition. If you, your partner, or a member of either of your families has a genetic condition, such as cystic fibrosis or sickle cell disease, you may want to have an amnio.

How is the test done?

Amniocentesis takes a few minutes.

First, your health care provider asks you to lie flat on your back. He uses ultrasound to find your baby, the placenta and pockets of amniotic fluid. He then cleans your belly with an antibacterial liquid that destroys germs on your skin.

Next, using ultrasound as a guide, your provider puts a thin needle through your belly and uterus into the amniotic sac. He uses the needle to remove about 1 to 2 tablespoons (1 ounce) of fluid.

Once the fluid sample is taken, your health care provider uses the ultrasound to check that your baby’s heartbeat is healthy.

The amniotic fluid sample is sent to a lab, where it is examined and tested. In the lab, your baby’s cells are separated from the amniotic fluid. If your baby is being tested for genetic problems, the cells are grown for about 10 to 12 days at the lab so that there are enough to check for problems. Test results usually are available within 2 weeks.

The lab may test your baby’s amniotic fluid for proteins like alpha fetoprotein (AFP). Measuring the amount of AFP can check if your baby has neural tube defects (NTDs). The neural tube is the part of a developing baby that becomes the brain and spinal cord. AFP levels are often higher if your baby has an NTD. AFP test results usually are available in a few days.

Are there any risks to having an amnio?

Some women find that having an amnio is painless. Others feel cramping when the needle enters the uterus, or pressure when the fluid is removed. One to 2 out of 100 women (1 to 2 percent) have cramping, spotting or leaking amniotic fluid after the test. Your provider may tell you to avoid intense activity and take it easy for the rest of the day.

Serious complications from amniocentesis are rare. However, the test does involve a small risk of miscarriage. According to ACOG, less than 1 in 200 women (less than 1 percent) have a miscarriage after amniocentesis.

What happens after the test?

In most cases, amnio results show that a baby is healthy and without birth defects. If the test shows that your baby does have a birth defect, talk to your provider about your options. For example, your baby may be able to be treated with medicines or even surgery before birth. Or there may be treatments or surgery he can have after birth. Knowing about a birth defect before birth may help you get ready emotionally to care for your baby. You also can plan your baby’s birth with your health care provider to make sure she gets any special care she needs right after she’s born.

What if you’re not sure about having an amnio?

Choosing to have an amnio is a personal decision. Talking with genetic counselors, your health care provider, and religious and spiritual leaders can help you make decisions about testing for birth defects during pregnancy.

Ask your provider about other prenatal test options and how you can find a doctor who is trained and experienced in offering specific tests. Learn as much as you can about any prenatal tests your provider recommends to make the right decisions for you and your baby.

How can you reduce risk of birth defects?

Learn what you can do to get healthy before and during pregnancy to help reduce your risk for birth defects and improve your chances of having a healthy pregnancy and a healthy baby.

Last reviewed: October, 2012