PRENATAL DIAGNOSIS - Chorionic Villus Sampling

Chorionic villus sampling (CVS) is a prenatal test that involves taking a small sample of tissue from the placenta, a structure in the uterus that provides blood and nutrients from the mother to the fetus, to test for chromosome abnormalities, such as Down syndrome and many others, and certain other genetic problems. Before having the test done, your genetic counselor and doctor will explain the conditions that can and cannot be detected using CVS tissue.

The chorionic villi are tiny projections of placental tissue that look like fingers and contain the same genetic material as the fetus. Testing may be available for other genetic disorders, depending on the family history and availability of lab testing at the time of the procedure.

CVS is usually performed at about 11 weeks of pregnancy. Unlike amniocentesis (another type of prenatal test), CVS does not provide information on neural tube defects, such as spina bifida. For this reason, women who undergo CVS also need a follow-up blood test called a maternal serum alpha-fetoprotein (AFP) level between 16 to 18 weeks of their pregnancy to screen for neural tube defects. It is also a good idea for them to have a detailed ultrasound at about 18 weeks to look at the spine of the fetus in particular for the same reason.

In our center, transcervical CVS is performed. This is a procedure in which a catheter is inserted through the cervix into the placenta to obtain the tissue sample. Removing the small amount of tissue does not affect the fetus’s ability to get the blood supply it needs from the placenta.

Bleeding, infection and miscarriage are uncommon after CVS. The rate of miscarriage is less than two percent.

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