A chorionic villus sampling (CVS) prenatal test checks cells from the placenta (which are identical to cells from the fetus) to see if they have a chromosomal abnormality (such as Down syndrome).
The test can be done from weeks 10 to 13 in a woman's pregnancy. It's a diagnostic test rather than a screening test. That means that it can tell for sure whether a baby will be born with a specific chromosomal disorder.
This test is offered to all pregnant women, but especially those whose babies are at higher risk for a chromosomal abnormality. These include pregnant women who are older, already have a baby with a chromosomal disorder, or have had an abnormal screening test.
A CVS is considered an alternative to an amniocentesis because it can be done earlier in pregnancy, giving expectant parents more time to receive counseling and make decisions. Unlike amniocentesis, CVS does not provide information on neural tube defects like spina bifida. The risks of CVS are higher than with amniocentesis, so the risks and benefits of the test must be weighed.
Most pregnant women who are not high risk will not need this test. But your health care provider may recommend this test if you:
The placenta provides nutrients from the mother to the fetus through the umbilical cord. Chorionic (kor-ee-AH-nik) villi are tiny finger-like units in the placenta. They have the same chromosomes and genetic makeup as the fetus.
During a CVS, some cells from the chorionic villi are removed and tested for chromosomal abnormalities such as Down syndrome, Tay-Sachs disease, and fragile X syndrome.
This test can be done two ways:
Some women find that CVS is painless. Others feel cramping, similar to period cramps, while the sample is taken. After the sample is taken, the doctor may check the fetus' heart rate. You should rest for several hours after the test.
Possible risks of this test include:
Chorionic villus sampling testing is done at 10 to 13 weeks.
Results are usually available within a few hours to a couple of days, depending on what the test is being used to look for.
Reviewed by: Thinh Phu Nguyen, MD
Date Reviewed: Jul 20, 2022