Amniocentesis

What is amniocentesis?

Amniocentesis is a test that may be done during pregnancy. A 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 cells 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 health care 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 an ultrasound scan or AFP blood test, show the baby might have a problem.
• You have had a previous pregnancy or child with a birth defect.
• 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, or cystic fibrosis.
• You have had 3 or more miscarriages.
• You have Rh-negative blood and the baby's father has Rh-positive blood.
• You took or were exposed to harmful drugs when you got pregnant.

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 usually done if you have a high-risk condition and the baby may need to be delivered early.

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

How do I prepare for amniocentesis?

It helps to have a full bladder, so you may need to drink a lot of water before the test. Follow any other instructions your health care 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. Your skin is numbed with an anesthetic. Your health care provider uses ultrasound images to help guide a long needle through your abdomen and uterus, away from the baby and to the area where the most amniotic fluid is. You may feel some discomfort when the needle is inserted into your abdomen. A small amount of fluid is withdrawn and sent to the lab for tests.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 genetic tests will be available in 2 to 4 weeks. Lung maturity can be determined in 1 or 2 days. The results of a test for infection will also be available in 1 to 2 days.

What are the benefits of this procedure?

This test:

• helps detect some birth defects caused by 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 health care 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 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% of women have problems. Problems that can occur are:

• excessive loss of blood
• 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 rare cases, an abnormal result may not be accurate.

When should I call my health care provider?

Call your provider right away if:

• You start having contractions or severe cramping. (It is normal to have some brief cramping.)
• You have bloody or liquid vaginal discharge that does not stop. (It is normal to have a little spotting or leaking.)
• 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.