Amniocentesis is a pre-natal outpatient diagnostic test that is used to determine the possible presence of birth defects. It is usually performed between the sixteenth and twentieth week of pregnancy.

Your doctor may suggest an amniocentesis test if you are 35 years or older, have had a previous child with birth defects, have a family history of genetic disorders, are scheduled for Cesarean birth, or are expected to have premature labor. Tests on the amniotic fluid and cells in the fluid can detect birth defects such as Down syndrome, spina (spine-a) bifida (biff-a- da), some forms of muscular dystrophy, and some brain and blood disorders.

During the procedure, the doctor determines the position of the baby by using an ultrasound. A local anesthetic is used to numb the skin. A needle attached to a syringe is then inserted through the abdomen into the amniotic sac to withdraw about one ounce of fluid. The fluid is analyzed to determine if there are any possible defects.