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What Is Amniocentesis?

Learn about amniocentesis, including how it is performed and why some pregnant women choose to have it performed.
Amniocentesis Diagnostic Test

What Is Amniocentesis?

Baby Talk

Amniocentesis is a diagnostic test that withdraws fluid from the sac surrounding the fetus to diagnose a number of birth defects.

Amniocentesis is a procedure used to withdraw a small amount of amniotic fluid (the fluid in the sac surrounding the fetus). Analyzing this fluid can help diagnose a number of birth defects with approximately 99 percent accuracy. This diagnostic test offers the most remarkable advancement of this century in prenatal care.

Amniocentesis is usually performed between weeks 15 and 18 of pregnancy. But it can be performed as early as Week 12 or as late as Week 20. It might also be performed toward the end of the pregnancy to check the baby's lung maturity. Depending on the tests being performed on the fluid, it can take anywhere from one day to one month to get the results.

Why Bother?

Amniocentesis is most commonly used to determine two things:

  • Chromosomal abnormalities. These are birth defects or genetic problems. The test can identify several hundred genetic disorders, including some of the most common ones, such as Down's syndrome, Tay-Sachs disease, or sickle-cell anemia. It can also identify neural tube defects, such as spina bifida (a deformity of the spinal column) or anencephaly (the absence of all or part of the brain).
  • The maturity of the baby's lungs. If there is a chance the baby will need an emergency early delivery, it is important to know if the lungs are mature enough to allow the baby to breathe or if she will need medical attention to assist with breathing.

Although the test is not given for this specific purpose, it can also tell the gender of the baby with great accuracy.

Daddy Alert!

Your family medical history is also very important in determining if your partner should undergo amniocentesis. Your genes share an equal part in creating the baby your partner is carrying. If you're not sure if you have a history of birth defects or inherited diseases, talk to other family members and get the facts.

Pregnancy Facts

Medical literature tells us that amniocentesis was performed as early as the nineteenth century. But it wasn't until 1966 that fetal cells could be grown and their genetic traits analyzed. Before the sixties, genetic birth defects were a surprise delivered at the birth of the baby.

To Have or Not to Have

No one is required to have this test. But an amniocentesis is generally offered to women in the following three categories:

  • Older women. Women over the age of 35 are at higher risk of having a baby with chromosomal disorders.
  • At-risk women. These are women who have received a positive result on their AFP test. This test can identify women whose babies are at risk for certain chromosomal problems.
  • Women who have a family history of certain birth defects (or women whose partners do).

Some women want to have an amniocentesis; others say no way. Those who have it want to know in advance if their baby has a birth defect; this gives them time to decide either to terminate the pregnancy or to learn more about the baby's future needs. Other women choose not to have this test because they will not consider having an abortion and prefer to learn about the baby's health at delivery. This is not always a wise decision; knowing in advance about a baby's medical problems allows the health care team and the parents to plan the safest timing, location, and method of delivery, with the appropriate specialists available immediately after birth. But nobody knows what's best for you, except you. This is a personal decision you should make with the help of your family, your doctor, and (if necessary) a genetic counselor.

Forewarned Is Forearmed

Nobody likes the thought of how an amniocentesis is performed, because it involves a long needle. But don't faint away just yet. Millions of women have had this test and have lived to tell the tale.

An amniocentesis is usually performed in a hospital. Here you will lie down on an examining table and the doctor or technician will use an ultrasound to locate the fetus and decide on the best place, away from the baby and the placenta, to insert the needle. This is not always a quick process, so lie back and relax. It can take up to about 20 minutes to find just the right spot.

The rest of the test is much faster. The doctor will take about five minutes to insert a long, thin, hollow needle through the abdominal wall and into the sac of amniotic fluid around the baby. As she does this, you're allowed to yell "Ouch!" (or shout any other word that comes to mind). It is not terribly painful, but most women say the needle stings as it goes in. The needle withdraws about two tablespoons of amniotic fluid and the test is over.

After the test, you may have some cramping and/or spotting. Your doctor will probably tell you to take it easy for the rest of the day. You will also be told to watch for signs of infection. About one woman out of 200 gets an infection, or some other complication that results in miscarriage after an amniocentesis. That's why it's so important to let your doctor know immediately if you experience fever, chills, contractions, irritability, and uterine tenderness after having this test.

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