What is an amniocentesis?

Amniocentesis is a prenatal test that is usually done between 15 and 20 weeks of pregnancy. It involves testing a very small sample of the amniotic fluid, the special fluid that surrounds your developing baby. Amniocentesis is called an invasive test because it requires going into your uterus (womb) to get the test sample.

Amniocentesis is a highly accurate way to determine if your pregnancy is affected by a genetic disorder such as Down syndrome, trisomy 18, or cystic fibrosis. It can also screen for neural tube defects such as spina bifida.
An amniocentesis is a screening that enables your health care professional to examine fetal cells in the amniotic fluid for any chromosomal abnormalities. The test is not routinely given under the age of 35, due to the small risk of miscarriage associated with this procedure—amniocentesis has a complication rate of less than 1 percent, but there is a small risk of miscarriage associated with it. If you are 35 or older when you're due to have your baby, your health care professional will likely discuss the risks of chromosomal abnormalities based on your age and recommend this test.

That's because women over 35 have a higher risk of having a baby with Down's syndrome. An amniocentesis is also recommended if you've already had a child with certain birth defects, or if you have a family or personal history that puts you at risk for certain inherited diseases. You might choose to have this test if you had abnormal blood tests that suggest there might be a problem.

Amniocentesis can diagnose numerous conditions, but only if the lab evaluating the amniotic fluid knows which tests to conduct. These tests are very expensive, so talk with your health care professional about which ones are necessary based on your history and risk factors. It can take anywhere from a few days to a few weeks to get the results.

During an amniocentesis, the doctor inserts a needle through your abdomen into the amniotic sac and removes a small amount of amniotic fluid. The doctor uses ultrasound to guide the needle and avoid inserting it into the placenta.

The test can be performed on an outpatient basis in a health care professional's office or in a hospital. It can be done at any gestational age after 11 weeks, but when it's performed for genetic studies, amniocentesis is usually done between 15 and 17 weeks.
Amniocentesis involves removing a small amount of amniotic fluid (water that surrounds the baby). The doctor uses ultrasound to help guide a thin needle through the mother's abdomen to get this fluid. This test is done after 15 1/2 weeks. Amniocentesis is most often used to detect Down syndrome and other chromosomal abnormalities, spina bifida, anencephaly and inherited metabolic disorders.
Amniocentesis is a prenatal screening test typically performed around 15 to 18 weeks of pregnancy. A small amount of fluid from the amniotic sac that surrounds the fetus is removed for testing to identify birth defects such as spina bifida, chromosome problems like Down syndrome, blood incompatibilities between the mother and baby such as Rh disease, fetal maturity, and the baby's gender. Results are available in about two weeks. An ultrasound is used during the procedure to watch both the position of the fetus and the insertion of a thin needle through the abdomen into the amniotic sac.
Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
Amniocentesis can detect genetic disorders before your baby is born.

Watch this video animation where Dr. Oz explains the amniocentesis procedure.

This test is performed between 15 and 20 weeks of pregnancy and can indicate chromosomal abnormalities such as Down syndrome, or genetic disorders such as Tay Sachs disease, sickle cell disease, cystic fibrosis, and others. It also can detect the baby's sex and risk of spina bifida (a condition in which the brain or spine do not develop properly).

This answer is based on source information from the U.S. Department of Health and Human Services.

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