Prenatal Testing Basics: CVS Test

What it is, who has it, when, why, and what it tells you.

By the editors of Parents magazine

When is the test taken?

Chorionic Villus Sampling (CVS) is usually performed between 10 and 12 weeks after your last menstrual period.

Who needs to take the test, and why?

CVS is used to get an early diagnosis of genetic and/or chromosomal abnormalities such as Down syndrome. It's offered when there's an increased risk of such defects, and when expectant parents want early test results instead of waiting to have an amniocentesis (which tests for many of the same abnormalities but is given only in the second trimester). You may be offered CVS if you will be 35 or older on your due date, have had a prior child with chromosomal or genetic abnormalities, or have a history of such problems in your family. If you feel strongly that you would rather have the option of terminating a pregnancy before the end of your first trimester, you should ask your doctor about this test as an alternative to amniocentesis. Be aware, however, that the CVS test carries a slightly higher risk of test-related miscarriage than amnio -- perhaps 1 in 100 for CVS as opposed to less than 1 in 200 for amnio. (Some medical sources say this risk could be as high as 3.5 or 4 in 100, but, to date, no controlled studies have been completed.) Also, you should be aware that CVS cannot test for neural tube defects.

What's involved?

Chorionic villus sampling begins with an ultrasound exam, which is needed to confirm the age of the fetus and the position of the placenta. Then, using the ultrasound image as a guide, the practitioner removes a tiny piece of the chorionic villi, the fingerlike projections of tissue that attach the placenta to the wall of the uterus. This can be done in one of two ways. (1) In a transcervical CVS, the practitioner inserts a narrow tube through the vaginal canal and into the cervix, using gentle suction to extract a bit of the needed tissue. (2) In a transabdominal CVS, a long, narrow needle is inserted through the abdomen and into the uterus to extract the tissue. The type of CVS your practitioner chooses to perform will depend on your individual anatomy and the position of the placenta. The villi sample (which shares the same genetic makeup as the baby) is sent to a lab, where it is grown in a culture, then checked for defects.

The test lasts about a half an hour, but the extraction process should only take a few minutes. It may be painless, or it may pinch or hurt briefly. Afterward, you should take it easy: plan to take the rest of the day off of work, arrange for a ride home, and relax. You may experience mild cramping and slight spotting. Any prolonged bleeding or cramping should be immediately reported to your healthcare provider.

When are test results available, and how are they interpreted?

Results are normally available within 7 to 14 days. CVS test results are more than 99 percent accurate in diagnosing many genetic and chromosomal abnormalities. If you receive "normal" results, your baby has an excellent chance of being healthy -- but be aware that the test doesn't rule out every possible problem. If your test results indicate an abnormality, you will meet with your practitioner and a genetic specialist to discuss your options, which may include further tests.