Maternal and Infant Health Program Maternal and Infant Health Program

  SLC area: (801) 273-2871

  SLC area: (801) 274-0674

  Maternal and Infant Health Program
  P.O. Box 142002
  Salt Lake City UT


There may be times during pregnancy when you or your prenatal care provider would like to know more about your baby’s health and development. One of the tests your doctor or midwife may recommend is amniocentesis. This article contains answers to common questions about amniocentesis.

What is Amniocentesis?
Amniocentesis is a prenatal test in which a small sample of amniotic fluid is taken out and tested. Amniotic fluid is the “water” that is around the baby inside the womb.

Why is Amniocentesis Done?
There are many tests that can be done using amniotic fluid:

  • Genetic Studies. By testing the cells found in the fluid, doctors can find genetic problems like Down syndrome. This test is usually done during the second trimester. Pregnant women who will be over age 34 on the baby’s due date, or who have a family history of genetic problems may consider genetic testing. It is also offered to women who have an abnormal alpha-fetoprotein test (also called multiple marker screen or triple screen). Knowing whether or not to expect a genetic defect can help parents and care providers prepare for the upcoming birth.
  • Lung Maturity. After the 32nd week of pregnancy, amniotic fluid can be tested to see if the baby’s lungs have matured enough for the baby to be born early. This is important if the mother has severe health problems such as high blood pressure. If the unborn baby’s lungs are not ready, the doctor or midwife will usually try to delay labor. If the lungs are ready, it is probably safe for the baby to be born.
  • Rh Sensitization. If there are problems between the mother and baby’s blood, studies may be done to check for fetal anemia. The results help the doctor decide whether or not the baby should be born early or given a blood transfusion. This problem is very rare.
  • Infection. Rarely, amniotic fluid may be checked for infection because the water has broken early or for other reasons. The fluid will help the doctor know which medicine will best fight the infection.

How is Amniocentesis Done?
Amniocentesis can be done at a clinic or hospital. First, the doctor uses ultrasound to find a pocket of fluid that is safely away from the baby and the placenta. The woman’s belly is then cleaned with iodine. Next, the doctor puts a long thin needle through the woman’s belly, into the amniotic sac. About one to two tablespoons of fluid is taken out, and the needle is pulled out. If the woman has twins, a sample is taken from each sac. Last, the baby’s heartbeat is checked. The test usually takes only a few minutes. Most women feel pressure and mild discomfort during amniocentesis.

What Should I Expect after the Amniocentesis?
After amniocentesis you should plan to take it easy and avoid heavy lifting, exercise and sex for one or two days. You may feel slight cramping for about a day. If your blood is Rh negative, you will get a shot of RhoGAM. Check with your doctor if you have fluid leaking from your belly, major cramping, spotting, or fever.

Is Amniocentesis Safe?
Problems after amniocentesis are rare, but may occur. It is up to you to decide whether or not you want to have an amniocentesis done. It is a good idea to talk about the risks and benefits of the test with your doctor, your partner, and/or a genetic counselor.

According to the Centers for Disease Control (CDC), the rate of miscarriage due to amniocentesis is 1 in 200 to 400 (or 1/4 to 1/2 of one percent). The risk of miscarriage goes down if it is done later in pregnancy. There is also a very low risk of infection in the uterus after the test (about one in 1,000). Rarely, the needle may touch the baby during the test, but it is usually harmless. Doctors use an ultrasound during the test to avoid touching the baby.

How Soon Will I Know the Results of the Test?
It depends on the type of test. Some tests for lung maturity are done in a few minutes. Genetic tests usually take about seven to ten days because the cells must be grown in a lab before they are tested.

What is the Difference Between Chorionic Villus Sampling (CVS) and Amniocentesis?
CVS is a test in which a few cells are taken from the place where the placenta meets the uterus. It is done between the 10th and 12th week of pregnancy. CVS helps doctors find genetic problems earlier than amniocentesis, but the test has a higher risk of miscarriage. It is a newer test than amniocentesis, so it isn’t offered in all areas. Also, CVS does not test for neural tube defects such as spina bifida.

If you have more questions about amniocentesis, contact your prenatal care provider. This article is for informational purposes only, and does not replace the advice of a doctor or certified nurse midwife.

Click here for a printer friendly version of this document.