Chorionic villous sampling (CVS) is a prenatal test that verifies severe chromosomal disorders in the developing baby. The test consists of taking a sample of the chorionic villi, part of the placenta, and analyzing the genetic constitution of the tissue. A small sample of placenta is taken transabdominally under ultrasound guidance. Chorionic villus sampling (CVS) can be taken earlier in pregnancy than amniocentesis (between 10 and 13 weeks of gestation). However, the result may be slightly less reliable than amniocentesis, due to the possibility of confined placental mosaic.

 

Like amniocentesis, CVS can identify:

• Almost all chromosomal abnormalities, including Down syndrome, Trisomy 13, trisomy 18 and sex chromosome abnormalities (such as Turner syndrome). The test can diagnose these conditions, but it can not measure their severity.
• Several hundred genetic disorders, such as cystic fibrosis, sickle cell anemia and Tay-Sachs disease. The test is not used to search for all of them.