McKesson Clinical Reference Systems: Women's Health Advisor 2002.2
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What is amniocentesis?

Amniocentesis is a procedure in which your health care provider uses a needle 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 in the uterus when you are pregnant. The sample of fluid is analyzed in the lab.

Amniotic fluid contains cells from the baby. Early in pregnancy the cells can be tested for certain genetic problems the baby might have. Amniocentesis is sometimes done near the end of a pregnancy to test the maturity of a baby's lungs.

When is it used?

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

Your health care provider may advise you to have amniocentesis in the following cases:

• You are over age 35.
• Prenatal tests show an increased likelihood of a problem with the baby.
• You have given birth to a child with Down syndrome or another genetic disorder.
• You or your baby's father have a family history of genetic problems.
• You have a child with a defect in the spinal cord or brain.
• You have had three or more miscarriages.
• You have Rh-negative blood and the baby's father has Rh-positive blood.

Amniocentesis may be done later in 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 procedure. 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 procedure. Your abdomen is cleaned with an antiseptic. Your skin is numbed with an anesthetic. Ultrasound helps your health care provider guide the 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 A small amount of fluid is withdrawn and sent to the lab for tests.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 procedure. Then you can go home. You should rest for 24 hours after the procedure.

The results of the genetic analysis will be available in 1 to 3 weeks. Lung maturity can be determined in 1 or 2 days. The results of a test for infection will be available in 1 to 2 days.

Women who have Rh-negative blood and are carrying Rh-positive babies may need a shot to prevent blood incompatibility problems.

What are the benefits of this procedure?

Amniocentesis:

• helps detect genetic problems, such as Down syndrome or other chromosomal abnormalities
• can detect development disorders such as spina bifida
• can detect infection in the amniotic fluid
• can check the maturity of the baby's lungs.

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. However, you should know what problems can occur. The following are possible complications of amniocentesis:

• excessive loss of blood
• infection in the amniotic fluid
• harm to the baby from the needle
• harm to the placenta or cord from the needle
• premature breaking (rupture) of the amniotic sac
• premature labor, or contractions that can cause labor
• miscarriage (less than 1 pregnancy is lost for every 200 genetic amniocentesis procedures performed).

It is important to understand that normal test results cannot guarantee that the baby will be normal.

When should I call my health care provider?

Call your health care 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 doesn't stop. (It is normal to have a little spotting or leaking.)
• You develop a fever.
• You have any changes related to the pregnancy that concern you.

Call your health care provider during office hours if:

• You have questions about the procedure or its result.
• You want to make another appointment.

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.