CVS is performed between 10 and 12 weeks of pregnancy. In CVS, the doctor inserts a needle through the abdomen or inserts a catheter through the cervix to reach the placenta. The doctor then takes a sample of cells from the placenta. Experts use this sample to look for problems with the baby's chromosomes. This test cannot find out whether your baby has open neural tube defects. About 1 in 200 women have a miscarriage as a result of this test.
Source: National Women’s Health Information Center, U.S. Department of Health and Human Services, www.womenshealth.gov