There are several reasons why an expectant mother would choose to have an amniocentesis, which is a test that examines fetal cells present in amniotic fluid with the purpose of detecting chromosomal disorders. The test is normally performed 15 to 18 weeks after the last menstrual period. The procedure also may be done late in pregnancy to determine if the fetus' lungs are developed prior to a medically necessary premature birth.

An amniocentesis can take place in a hospital or in a doctor's office. While lying on her back, a needle is inserted into the mother's abdomen while an ultrasound reveals the location of the fetus. It is important that the needle does not reach the fetus. Amniotic fluid is withdrawn through the needle and used for testing. Test results take one to two weeks because it is necessary for the cells to grow and develop in a lab. In the event of an amniocentesis to determine lung growth only, results are available within a few hours. While the procedure poses no risk to the mother's health, the Centers for Disease Control and Prevention estimate the rate of miscarriage after an amniocentesis is between one in 200 and one in 400. Some women experience pain during the needle injection and other women feel no discomfort at all. According to the American Association of Family Physicians, some women will experience mild cramping after the procedure.

An amniocentesis is truly an amazing test. By testing a few teaspoons of amniotic fluid, the test not only can detect chromosomal abnormalities and lung development, it can also determine Rh disease (Rh factor incompatible with mother's blood), fetal anemia and the baby's sex. However, there are several abnormalities and health conditions that cannot be detected by the procedure, and a clear test result does not guarantee a healthy baby.

"Amniocentesis is not a medical miracle," says Dr. Aliza Kolker, professor of sociology at George Mason University. "It cannot cure abnormalities but merely diagnoses them." Kolker is the author of Prenatal Testing and many articles on the subject.

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