What Is Chorionic Villus Sampling?

Chorionic villus sampling (CVS) is a diagnostic test that can identify or rule out certain birth defects. It is similar to an amniocentesis, with one major advantage: It can be done as early as the 9th week of pregnancy. This difference becomes important if the test reports the presence of a birth defect and the parents wish to have an abortion. It is always best to have an abortion as early in the pregnancy as possible.

An amniocentesis is rarely performed before the 12th week, and it can take several more weeks to learn the results. This long wait makes medically necessary abortions much more difficult both emotionally and physically.

CVS is not routinely offered to all pregnant women. Like amniocentesis, it carries the risk of miscarriage and possibly other complications such as limb abnormalities if performed before the 10th week. But it is an option for women who fit into one of these categories:

• Women over age 35. The risk of bearing a child with certain chromosomal birth defects increases as a woman ages.
• Women with a history of bearing a child (or children) with a birth defect.
• Women whose family medical history shows their children may be at risk for inheriting a genetic disorder.

CVS is generally performed in a hospital. Like an amniocentesis, ultrasound monitoring picks up the location and position of the fetus and placenta. A catheter (a small tube that's attached to a syringe) is used to extract the needed cells, but instead of taking amniotic fluid, the doctor will take a sampling of cells from the placenta.

The entry is first swabbed with an antiseptic solution to prevent infection. Then the doctor inserts either a catheter into the vagina through the cervix, or a needle through the abdomen, in order to obtain a tiny piece of chorionic villi (fetal cells of the placenta) for analysis. No anesthetic is given because this test is not painful. However, some women say they feel a pinch when the sample is taken.

After amniocentesis, you may feel some cramping and have some spotting, but this should stop within a few days.