Chorionic villus sampling

Chorionic villi sampling (CVS): what it tests for and how it’s performed

Chorionic villi sampling (CVS) testing is a prenatal diagnostic procedure performed in the first trimester, usually starting at 10 weeks.

CVS tests for:                                                 

  • Fetal chromosome abnormalities. The most common chromosome abnormality is Down syndrome, caused by an extra copy of chromosome 21 (known as trisomy 21). The next most common chromosome abnormalities are trisomy 18 and trisomy 13.
  • Specific inherited diseases when parents have been shown to be carriers of the specific disease. Examples include Tay-Sachs disease, cystic fibrosis and spinal muscular atrophy.

 

How the test is performed

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.

 

Understanding results

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.