Chorionic villus sampling (CVS) is a test done during early pregnancy that can find certain problems with your baby (fetus). It is generally done when either you or the father has a disease that runs in the family (genetic disorder). It may also be done when you are over age 35-being over 35 increases your chance of having a baby with a chromosome defect.

Chorionic villi are tiny fingerlike growths found in the placenta. The genetic material in chorionic villus cells is the same as that in the baby's cells. During CVS, a sample of the chorionic villus cells is taken for biopsy. The chorionic villus cells are checked for problems. The procedure is generally done late in the first trimester, most often between the 10th and 12th weeks. CVS generally is not done after the 13th week of pregnancy because there is more amniotic fluid around the baby which makes it harder to do the procedure.

The chorionic villus sample can be collected by putting a thin flexible tube (catheter) through the vagina and cervix into the placenta. The sample can also be collected through a long, thin needle put through the belly into the placenta. Ultrasound is used to guide the catheter or needle into the correct spot for collecting the sample.

CVS can find hundreds of family diseases, such as Tay-Sachs disease or hemophilia. It can also find chromosomal birth defects, such as Down syndrome. CVS cannot find neural tube defects and it cannot be used to see if the baby's lungs are mature.

Chorionic villus sampling can be done earlier in pregnancy (at 10 to 12 weeks) than amniocentesis (usually done at 15 to 20 weeks). This allows you to know the health of your baby and make an earlier decision whether to continue or end the pregnancy. Results of CVS can be available sooner than amniocentesis results.

Should I have chorionic villus sampling?

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Why It Is Done

Chorionic villus sampling (CVS) is done to:

• Find family genetic problems (such as Tay-Sachs disease, hemophilia, sickle cell disease, cystic fibrosis, or thalassemia) of your baby during pregnancy, especially if either you or the father has a family history of a genetic problem.
• Find chromosomal birth defects (such as Down syndrome), especially if you are over age 35.
• Find out the sex of your baby if you know you might have a sex-linked genetic disorder. For example, hemophilia can be passed from a mother (who does not have the disease) only to her male children. Her female children may be carriers of the disease but will not have the disease.
• Find the blood type of your baby when Rh sensitization has occurred.
• Find the cause of a miscarriage, especially if you have had more than one.