CVS stands for chorionic villus sampling, a test performed in the first trimester (usually between weeks 10 and 12) to assess chromosomal abnormalities and hereditary conditions in the unborn baby. Your provider will use ultrasound guidance to insert a catheter into the placenta, either through the cervix (transcervical) or through a needle injected into the abdomen (transabdominal). The catheter is used to extract a biopsy (or sample) of the tiny chorionic villi, the fingers of tissue surrounding the embryo that are the beginnings of the placenta. The villi are a genetic match for the baby's own tissue.

Slight cramping and spotting is normal after the procedure, and you will probably be advised to indulge in some rest and relaxation for the remainder of the day. If bleeding continues, is excessive, or is accompanied by pain or fever, call your practitioner immediately.

A CVS is not always accurate. The exact spot where the technician removes the cell sampling from the chorion can be critical. Also, some abnormalities in chorionic tissues do not always show up in the fetus. Ask for clarification or a second opinion of any negative CVS report before you decide on any course of action in your pregnancy.

CVS has several benefits over amnio. It can be performed earlier (first trimester as opposed to second) and the results are available much faster (five to seven days for preliminary CVS results versus ten to fourteen days for amnio). However, the risk of miscarriage is higher with CVS — between one in 200 and one in 100 will experience miscarriage after the procedure. The risk is higher for women with a retroverted (tipped or tilted) uterus who are given a transcervical CVS (about five in 100). For this reason, a transabdominal CVS (through the abdominal wall) is usually advised for these women. A consultation with a genetic counselor can help you analyze the positives and negatives and decide whether a CVS is right for you.