Definition of Amniocentesis:

Amniocentesis is a test during pregnancy that removes a small amount of fluid from the sac around the baby to look for birth defects and chromosome problems.

How the test is performed:

Amniocentesis is done on an outpatient basis. You do not need to stay in the hospital.

The doctor will find the exact location of the baby, usually by performing a pregnancy ultrasound.

The health care provider will clean an area of skin on the mother's belly area. A numbing medication (anesthetic) may be applied to the skin, or a local anesthetic may be injected into the skin.

The doctor inserts a long, thin needle through the abdomen and into the womb (uterus). A small amount of fluid is taken from the fluid-filled sac that surrounds the baby.

How to prepare for the test:

Your bladder must be full for the ultrasound. There are no food or drink restrictions.

You may need to provide a blood sample to determine your blood type and Rh factor. You may get an injection of a medication called Rhogam if you are Rh negative.

You will need to sign a consent form before the test.

How the test will feel:

If an anesthetic is used, you may feel a sharp, stinging sensation for a few seconds. When the needle enters the amniotic sac, you may feel a sharp pain lasting a few seconds.

Some women feel pressure in the lower abdomen when the fluid is pulled out. After the procedure, you may have some minor cramping.

Why the test is performed:

The test can find chromosome problems such as:

• Anencephaly
• Down syndrome
• Rare, inherited metabolic disorders
• Spina bifida and other structure problems

Later on in a pregnancy, the test may be used to find problems such as:

• Infection
• Rh incompatibility

This test is also sometimes done later in pregnancy to determine whether the baby's lungs are developed if there is a condition that requires early delivery.