Amniocentesis is traditionally performed between 16 and 20 weeks of pregnancy. In certain high-risk pregnancies, early amniocentesis can be performed beginning at 12weeks, 4 days gestation. When amniocentesis is performed during the optimum time frame the risk of miscarriage, as well as other complications (such as infection, bleeding or membrane rupture), is small.
Amniocentesis is typically performed for maternal age (35 years or older), fetal abnormality noted on ultrasound, abnormal prenatal testing result, or paternal family history of inherited disease.
Amniocentesis involves using a thin needle to take a small sample of the amniotic fluid from the amniotic sac. Ultrasound guidance is used for the procedure. The procedure takes a few minutes to perform and most women report that it is painless although some women report and pressure or cramping sensation. Any residual discomfort usually resolves within a few hours after the procedure.
Fetal chromosome studies resulting from amniocentesis are considered to be nearly 100% accurate. Full results are available within 7 to 10 calendar days and preliminary results, for some conditions via a DNA probe, can be available within 48 hours.