This article waslast modified on January 5, 2018.

This test is not routinely performed but may be discussed with or offered to pregnant women who are at an increased risk of having a baby with certain chromosome disorders, such as Down syndrome, or genetic abnormalities, such as cystic fibrosis. Between the tenth and twelfth week of pregnancy, a chorionic villus sampling (CVS) procedure can be performed in which either a needle inserted through the woman’s abdomen or a tube inserted through the woman’s vagina and cervix is used to obtain a tissue sample from the placenta. These cells have the same genetic makeup as the fetus and are analyzed for chromosome disorders and gene abnormalities.