Amniocentesis

What is amniocentesis?

Amniocentesis is a test that may be done during pregnancy. 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 sample of amniotic fluid is tested in the lab. The fluid contains floating cells that come from the baby. Early in pregnancy the cells can be tested for some genetic problems the baby might have. Sometimes the test is done near the end of a pregnancy to check the development of a baby's lungs.

When is it used?

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

Amniocentesis 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 providers think that the baby would benefit by delivering 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?

There are no specific instructions needed before having 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 an antiseptic. 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 and uterus, away from the baby and to the area where the most amniotic fluid is. You may feel some brief and mild discomfort when the needle is inserted into your abdomen. A small amount of fluid (1 to 2 tablespoons) is withdrawn and sent to the lab for tests.

If you are pregnant with more than one baby, a sample of fluid will be taken from each baby's amniotic sac.

What happens after the procedure?

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

The results of the most common genetic tests will be available in 2 weeks. Lung maturity can be determined faster, usually within one day. The results of a test for infection will take a little longer depending on the type of infection.

What are the benefits of this procedure?

This test:

• Helps detect some birth defects caused by many different types 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, if you want to know.

If the test finds a chromosome or genetic problem, you and your healthcare provider can discuss your options for treatment. For example,

• Some birth defects can be treated before the baby is born.
• You may be able to plan your delivery in a center equipped to deal with birth defects.
• You can get help, such as genetic counseling, that will help you prepare for the baby's problems. There are also many support groups for families who have children with birth defects.

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 will 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)

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 of 100°F (37.8°C) or higher.
• 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.