Pregnancy and Childbirth What to Expect During Amniocentesis By UPMC Magee-Womens Hospital, May 2, 2015 During pregnancy, you will undergo many tests and evaluations to ensure you and your baby are healthy and developing properly. One test you have the option to get is an amniocentesis. This is a big decision, as the results may influence the rest of your pregnancy. What Is Amniocentesis? An amniocentesis is a medical test done usually between the 16th and 22nd week of pregnancy. It looks for certain health conditions in your baby. The test can detect many conditions, including: Down Syndrome Sickle cell disease Cystic fibrosis Muscular dystrophy Tay-Sachs and similar disorders It also looks for signs of brain and spine problems such as anencephaly (open skull) and spina bifida (open spine). How Is the Amniocentesis Test Performed? An amniocentesis is completed during an ultrasound. A needle is inserted through the belly and the wall of the uterus to take a small amount of amniotic fluid. Amniocentesis occurs during an ultrasound to make sure the needle stays away from the baby and placenta. The fluid is then tested to look at the baby’s chromosomes. Usually, each cell has 46 chromosomes. Too many or too few can result in health problems. The test also looks at the alpha-fetoprotein (AFP) in the fluid to detect brain and spine problems. An amniocentesis is about 99.4 percent accurate in predicting health conditions with the baby. It carries a small risk of miscarriage — about 1 in every 1,000 procedures. When Is Amniocentesis Recommended? An amniocentesis is offered to every woman during pregnancy, but the procedure may be recommended for women who are at high risk of genetic diseases. For example, if you have a family history of birth defects or a child with a birth defect, your doctor may suggest the test. Women over age 35 or who have an abnormal ultrasound may also consider an amniocentesis. You always have a choice about whether or not to get an amniocentesis. Birth defects are rare, occurring in only 2 to 3 percent of births. The test only detects chromosomal abnormalities, which account for an even smaller percentage of birth defects. When trying to decide whether to get an amniocentesis, you may want to speak with a genetic counselor in addition to your doctor to review the risks and benefits. To learn more about genetic testing, visit Magee-Womens Hospital of UPMC. Want to learn more about maternal fetal medicine and preterm birth? Check out our Medical Monday’s post on Newborn Medicine.