Chorionic villus sampling (CVS) is a prenatal test that is used to detect birth defects, genetic diseases, and other problems during pregnancy. During the test, a small sample of cells (called chorionic villi) is taken from the placenta where it attaches to the wall of the uterus.

Chorionic villi are tiny parts of the placenta that are formed from the fertilized egg, so they have the same genes as the baby.

You may be offered CVS if you have certain risk factors for having a baby with a birth defect or genetic disease, so that problems can be found early in pregnancy.

What Diseases or Disorders Can CVS Identify?

CVS can help identify such chromosomal problems as Down syndrome or other genetic diseases such as cystic fibrosis, Tay-Sachs disease, and sickle cell anemia. CVS is considered to be 98% accurate in the diagnosis of chromosomal defects. The procedure also identifies the sex of the fetus, so it can identify disorders that are linked to one sex (such as certain types of muscular dystrophy that occur most often in males).