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.
Why Is Chorionic Villus Sampling Done?
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.
Should I Have a CVS?
Most pregnant women who are not high risk will not need this test. But your health care provider may recommend this test if you:
are age 35 or older
have a family history of genetic disorders (or a partner who does)
have a previous child with a genetic disorder or had a previous pregnancy with a chromosomal abnormality
have had an earlier screening test that indicates that there may be a concern
What Happens During CVS?
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.
Transcervical: Using ultrasound as a guide, a thin tube is passed from the vagina into the cervix. Gentle suction removes a sample of tissue from the chorionic villi.
Transabdominal: A needle is inserted through the abdominal wall with ultrasound guidance and a sample of the chorionic villi is removed.
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:
about a 1% risk of miscarriage (the risk is higher with the transcervical method)
spotting or bleeding (this is more common with the transcervical method)
rarely, defects to the baby's fingers or toes if the test is done too early in pregnancy
When Is CVS Done?
Chorionic villus sampling testing is done at 10 to 13 weeks.
When Are the Results Available?
Results are usually available within a few hours to a couple of days, depending on what the test is being used to look for.