Pregnant women considered to have a high risk of carrying a fetus with chromosomal or genetic abnormalities can confirm the diagnosis with diagnostic testing procedures like chorionic villus sampling (CVS) or amniocentesis. These procedures involve removal of placental cells (CVS) or the fluid that surrounds the fetus (amniocentesis). Typically, CVS is done at 10-14 weeks’ gestation and amniocentesis is done at 16-20 weeks’ gestation. The most serious complication of these procedures is miscarriage. For every 100 women who undergo CVS, approximately one woman will have a miscarriage as a result of the procedure. Amniocentesis can also cause miscarriage though the risk is lower than with CVS.