Chorionic villi sampling (CVS) testing is a prenatal diagnostic procedure performed in the first trimester, usually starting at 10 weeks.
Before and during the procedure, the doctor performs an ultrasound to show a picture of the uterus, the placenta and the fetus on a monitor. Depending on the position of the placenta and fetus, the doctor uses one of two approaches to obtain the chorionic villi sample (the chorionic villi are part of the placenta), either through the cervix (transcervical) or through the abdomen (transabdominal).
The sample of chorionic villi is then sent to the laboratory for an analysis for certain birth defects and genetic disorders.
Since the chorionic tissue and the fetus originate from the same fertilized cell, they are usually genetically the same. However, in approximately 1 in 100 cases, the results can be difficult to interpret. In this case, a follow-up amniocentesis may be offered. If your results are abnormal, you should talk with your doctor or with a genetics specialist about the meaning of your results.