Your Guide to Prenatal Tests

Chorionic Villus Sampling (CVS)

Who: Women over 35 and those who have—or whose partners have—a family history of genetic diseases such as cystic fibrosis

When: Between 10 and 13 weeks

How: Using ultrasound as a guide, a doctor inserts a catheter through the cervix or a needle into the abdomen to retrieve sample cells from within the chorionic villi, which are tiny parts of the placenta.

Why: To test for genetic disorders such as Down syndrome, sickle cell anemia, and cystic fibrosis.

Results and follow-up: The results, which are more than 99 percent accurate, are generally available within seven to ten days. A faster test, known as "FISH" (fluorescent in situ hybridization), can quickly check for five major chromosomal abnormalities, including Down syndrome; this test gives results in two or three days. The main advantage of CVS is that it can be done early in the pregnancy, but it does carry a (roughly) one in 400 risk of miscarriage (the same risk as for amniocentesis). Additionally, you’ll need to be on bedrest for 24 to 48 hours after the procedure with activity restrictions for a week.