Chorionic Villus Sampling (CVS)

Chorionic villus sampling (CVS) is a genetic test done during pregnancy. This test checks chorionic villus cells to see if your baby has certain health conditions. Chorionic villus cells are found in the placenta (the organ that brings oxygen and nutrients to the baby).

The test looks for abnormalities in your baby's chromosomes. Chromosomes are tiny 'packages' in your cells that contain your genes. Genes carry information, called DNA, that controls what you look like and how your body works.

Normally, you're born with a set of 46 chromosomes, with one set coming from each parent. The chorionic villi cells in the placenta contain the same chromosomes as your developing baby. So, a CVS test can show if your baby has an extra chromosome or a missing or damaged chromosome.

These chromosome differences can cause serious health problems. CVS is a prenatal diagnostic test, which means it can almost always tell for sure whether a developing baby has a chromosome disorder. This is different than a prenatal screening test, which only shows whether a baby has an increased risk of a serious health problem.

Why this test is done

A CVS test is not a routine pregnancy test. But your health care provider may recommend CVS testing if you are at higher risk for having a baby with a chromosome disorder. The risk factors include:

• Your age. If you are age 35 and older, you have a higher risk of having a baby with Down syndrome or another genetic disorder.
• A family history of a genetic disorder.
• Having another child with a genetic disorder.

You may also need CVS testing if you had abnormal results on a prenatal screening test.

How to prepare

On the morning of the test, you may be asked to drink extra fluids and not urinate. This will fill your bladder, which may help move the uterus into a better position for the procedure.

Other names for this test

CVS test