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What is amniocentesis?

Amniocentesis is a test that may be done during pregnancy to check the health of your baby. A very thin needle is used to remove a small amount of fluid from the amniotic sac. The amniotic sac is a thin sac filled with fluid that surrounds the baby. The fluid contains cells that come from the baby, as well as other substances. These cells and substances can be tested in the lab to give information about the health of the baby.

When is it used?

Early in pregnancy the cells can be tested for some genetic problems the baby might have. Your healthcare provider may advise you to have this test at this time if:

  • You will be 35 or older on the baby's due date.
  • Other tests, such as first-trimester genetic screening (combined ultrasound and blood testing), an ultrasound scan later in pregnancy, or one of your blood tests (AFP or triple or quad screen), show the baby might have a problem.
  • You have had a previous pregnancy or child with certain birth defects.
  • You or the baby's father has a family history of genetic problems, such as Down syndrome, fragile X syndrome, Tay-Sachs, sickle cell anemia, thalassemia, cystic fibrosis, and others.
  • You have had 3 or more miscarriages.
  • You have Rh-negative blood and the baby's father has Rh-positive blood.

When the test is used to check for genetic problems, it is usually done between the 15th and 18th weeks of pregnancy.

The test may be done toward the end of pregnancy to see if the baby's lungs are mature enough for the baby to breathe well after birth. This is sometimes done if you have a high-risk condition and your healthcare provider thinks that it may be best to deliver the baby earlier than your due date.

Amniocentesis can also be used to check for an infection in the amniotic fluid.

How do I prepare for amniocentesis?

You usually do not have to do anything to prepare for an amniocentesis early in pregnancy.

If the procedure is being done near your due date, your healthcare provider may advise you to avoid eating or drinking anything the day of the test.

Follow any other instructions your healthcare provider gives you.

What happens during the procedure?

The baby's heart rate is checked before and after the test. Your abdomen is cleaned with a liquid antiseptic solution. It is usually not necessary to use numbing medicine before performing this test.

Your healthcare provider uses ultrasound images to help guide a thin needle through your abdomen, into the uterus, away from the baby, and to the area where the most amniotic fluid is. Like when you have your blood drawn, you may feel some brief and mild discomfort when the needle is inserted into the skin of your abdomen. A small amount of fluid (1 to 2 tablespoons) is withdrawn into a syringe and sent to the lab for tests.

If you are pregnant with more than 1 baby, a sample of fluid may be taken from each baby's amniotic sac. This is done with different needles through your skin.

What happens after the procedure?

Your pulse, your blood pressure, and the baby's movements will be watched for a brief time after the test. Then you usually can go home. You should rest for 24 hours after the test.

The results of most of the genetic tests will be available in 1 to 2 weeks. Lung maturity can be determined faster, usually from 6 hours to 1 day. The results of a test for infection may take a few hours. It will take up to a few days if a culture is needed to check for certain bacterial infections.

What are the benefits of this procedure?

This test:

  • Helps detect some birth defects caused by a number of genetic problems, such as Down syndrome.
  • Can detect neural tube or spinal defects such as spina bifida.
  • Can detect infection in the amniotic fluid.
  • Can check the maturity of the baby's lungs.
  • Can find out if the baby is male or female, which may be important to know for some possible problems.
  • If the test finds a genetic problem, you and your healthcare provider will discuss your choices for treatment. The information can help you decide how to manage a pregnancy with a baby that may be affected by the problem.

What are the risks associated with this procedure?

The overall risk of complications from this procedure is very low. Less than 1 out of 200 women who have the test may develop a problem. Problems that can occur are:

  • bleeding
  • infection
  • harm to the baby, placenta, or umbilical cord by the needle
  • premature breaking (rupture) of the amniotic sac
  • premature contractions or labor
  • miscarriage (less than 1 pregnancy is lost for every 200 amniocentesis tests that are done)
  • injury to a nearby organ

It is important to understand that normal test results cannot guarantee that the baby will be normal. Also, in very rare cases, an abnormal result may not be accurate.

When should I call my healthcare provider?

Call your provider right away if:

  • You start having contractions or increased cramping. (It is normal to have some brief cramping for 4 to 6 hours after the test.)
  • You have bloody or liquid vaginal discharge that does not stop.
  • You develop a fever over 100°F (37.8°C).
  • Your baby is moving less than before the amniocentesis.
  • You have any changes related to the pregnancy that concern you.

Call during office hours if:

  • You have questions about the test or its result.
  • You want to make another appointment.
Developed by Phyllis G. Cooper, RN, MN, and RelayHealth.
Published by RelayHealth.
Last modified: 2010-06-14
Last reviewed: 2010-12-01
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2011 RelayHealth and/or its affiliates. All rights reserved.
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