Chorionic Villus Sampling

Chorionic villus sampling (CVS) is an early prenatal diagnostic test used to identify chromosome abnormalities, and it can also be used to identify certain other genetic disorders in the baby as early as 10-12 weeks of pregnancy. The test is performed by guiding a thin, flexible tube (“catheter”) through the woman’s vagina and cervix to the early placenta. A very small sample of placental tissue (chorionic villi) is obtained for laboratory analysis. This chorionic villi originates from the fertilized egg and thus has the same genetic makeup as the fetus.

The test will detect over 99 percent of chromosome abnormalities (such as Down syndrome). There are some preliminary evaluations that must be performed by the doctor before CVS can be done. Follow-up ultrasound at 18-20 weeks and serum AFP at 15-20 weeks are recommended. There are risks involved with the CVS procedure, therefore, a genetic counselor can discuss the benefits, risks, and limitations of prenatal diagnosis with individuals who may be indicated.