During pregnancy, the fetus is surrounded by amniotic fluid, a substance that is similar to water. Amniotic fluid contains fetal cells that are normally shed during growth, and other substances, such as alpha-fetoprotein (AFP). These substances provide important information about fetal health before birth.

What is amniocentesis?

Amniocentesis is a procedure in which a small amount of amniotic fluid is removed from the sac surrounding the fetus and is tested. The sample of amniotic fluid (less than one ounce) is removed through a fine needle inserted into the uterus through the abdomen, under ultrasound guidance. The fluid is then sent to a laboratory for analysis. Different tests can be performed on a sample of amniotic fluid, depending on the genetic risk.

Why is an amniocentesis performed?

Amniocentesis is performed to determine certain types of birth defects, such as Down syndrome (a chromosomal abnormality). Because genetic amniocentesis presents a small risk for both the mother and her baby, it is generally offered only to women who have a significant risk for genetic disorders, including those who:

  • Have an abnormal ultrasound or triple check value
  • Have a family history of certain birth defects
  • Have previously had a child with a birth defect
  • Will be older than age 34 at the time of delivery

Amniocentesis does not detect all birth defects, but it can be used to detect the following conditions, if the parents have a significant genetic risk:

Amniocentesis also can detect certain neural tube defects (development disorders of the brain and spinal column) such as spina bifida and anencephaly.

Because ultrasound is performed at the time of amniocentesis, it may find birth defects that are not detected by amniocentesis (such as cleft palate, cleft lip, club foot, or heart defects). There are some birth defects, however, that will not be detected by either amniocentesis or ultrasound.

When is amniocentesis performed?

If your doctor has recommended an amniocentesis, the procedure is usually scheduled between the 15th and 18th week of pregnancy.

How accurate is amniocentesis?

The accuracy of amniocentesis is about 99.4%.

Amniocentesis may occasionally be unsuccessful because of technical problems, such as an inability to collect an adequate amount of amniotic fluid or failure of the collected cells to grow when cultured.

Does amniocentesis have risks?

There is a small risk that an amniocentesis could cause a miscarriage (less than 1%, or approximately 1 in 200 to 1 in 400). Injury to the baby or mother, infection, or Rh isoimmunization are other potential complications, but are extremely rare.

Can I choose not to have an amniocentesis?

Yes. You will receive genetic counseling before the procedure. After the risks and benefits of amniocentesis have been thoroughly explained, you can choose whether or not you want to have the procedure.

What happens during an amniocentesis?

A small area of the abdomen is cleansed with an antiseptic. You may receive a local anesthetic (pain-relieving medication) to reduce any discomfort. Guided by ultrasound, the physician first locates the position of the fetus and placenta. Under ultrasound guidance, the physician inserts a thin, hollow needle through your abdomen and uterus, and into the amniotic sac, away from the fetus. A small amount of fluid (less than an ounce) is removed through the needle and sent for laboratory analysis.

You may feel minor menstrual-like cramping or discomfort; this is not unusual during the procedure or for a few hours after the procedure.

Can I resume normal activity after an amniocentesis?

After an amniocentesis, it is best to go home and relax for the remainder of the day. You should not exercise or perform any strenuous activity, and you should avoid sexual relations.

You may take two acetaminophen (Tylenol) every 4 hours if needed to relieve discomfort. The day after the procedure, you may resume all of your normal activities.

When should I call my doctor?

After an amniocentesis, call your doctor if you develop a fever or have bleeding, vaginal discharge, or abdominal pain greater than just mild cramps.

When will I receive the results?

The results of the amniocentesis are usually available in two to three weeks. If you have not heard from your doctor's office within 3 weeks, please call your obstetrical health care provider.