During pregnancy, the fetus is surrounded by amniotic fluid, a substance much like water. Amniotic fluid contains live fetal cells and other substances, such as alpha-fetoprotein (AFP). These substances provide important information about your baby's health before birth.
What Is Amniocentesis?
Amniocentesis is a prenatal test in which a small amount of amniotic fluid is removed from the sac surrounding the fetus for testing. 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 and indication for the test.
Why Is an Amniocentesis Performed?
A complete anatomical ultrasound will be done prior to amniocentesis. but amniocentesis is performed to look for certain types of birth defects, such as Down syndrome, a chromosomal abnormality.
Because amniocentesis presents a small risk for both the mother and her baby, the prenatal test is generally offered to women who have a significant risk for genetic diseases, including those who:
- Have an abnormal ultrasound or abnormal lab screens
- Have a family history of certain birth defects
- Have previously had a child or pregnancy with a birth defect
- Had an abnormal genetic test result in the current pregnancy
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 can detect certain neural tube defects (diseases where the brain and spinal column don't develop properly), such as spina bifida and anencephaly.
Because ultrasound is performed at the time of amniocentesis, it may detect 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.
If you are having an amniocentesis, you may ask to find out the baby's sex; amniocentesis is the most accurate way to determine the baby's gender before birth. However, you may already know the baby's gender from an earlier ultrasound or genetic test.
Although it's rarely performed in the third trimester, an amniocentesis can determine if the baby's lungs are mature enough for delivery, or to evaluate the amniotic fluid for infection.
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 due to technical problems, such as being unable to collect an adequate amount of amniotic fluid or failure of the collected cells to grow when cultured.
Does Amniocentesis Have Risks?
Yes. There is a small risk that an amniocentesis could cause a miscarriage (less than 1%, or approximately 1 in 1000 to 1 in 43000). Injury to the baby or mother, infection, and preterm labor are other potential complications that can occur, 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 to you, 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 to prepare for the amniocentesis. You may receive a local anesthetic (pain-relieving medication) to reduce any discomfort. The doctor first locates the position of the fetus and placenta with an ultrasound. Under ultrasound guidance, the doctor inserts a thin, hollow needle through your abdomen and uterus, and into the amniotic sac, away from the baby. 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 during the amniocentesis or for a few hours after the procedure.
Can I Resume Normal Activities 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, lift anything over 20 pounds (including children), and you should avoid sexual relations.
When Should I Call My Doctor After an Amniocentesis?
When Will I Receive the Results of the Amniocentesis?
The results of the amniocentesis are generally available within 2-3 weeks. If you have not received the results within 3 weeks, call your healthcare provider.