Chorionic Villus Sampling

CVS is usually performed by an obstetrician (OB) between the 11th and 14th weeks of pregnancy. The procedure takes about 20 minutes and is followed by a 30-minute resting period.  

During the procedure, the OB will use ultrasound to check on the fetus and guide the CVS. There are two approaches that can be used to collect the tissue sample, either through the vagina or through the abdomen.

Using the vaginal approach, a thin tube will be carefully inserted through the vagina and cervix into the uterus to collect a small sample of tissue from the placenta.

Using the approach through the abdomen, the OB will insert a thin needle through your belly into the uterus to get a small sample of tissue from the placenta.  

If you have an Rh-negative blood type, you will also receive a Rho(D) immune globulin injection at the time of the procedure. This prevents the development of antibodies that can harm the fetus.

Some patients may experience light cramping or spotting after the procedure. We recommend you avoid lifting or standing on your feet for extended periods of time for the next several hours after the procedure.

The collected placental tissue contains the same genetic information as the fetus. This tissue is grown (cultured) in a laboratory and then tested for certain genetic conditions.  

Your health-care provider will call you within two weeks to explain your test results.

Serious risks associated with CVS are rare and may include the following:

• A one per cent increase in the risk of miscarriage
• Spotting or cramping in the first two days after the procedure
• Rarely, the possibility of developing an infection

Call your primary care provider or visit the nearest emergency room if you experience a fever, bleeding or persistent cramping after CVS.

While there have been some reports linking CVS to limb abnormalities in fetuses, the World Health Organization reports that there is no increased risk when CVS is performed by an experienced physician after 10 weeks of pregnancy.

While CVS is a valuable diagnostic tool, it does not provide a complete picture of all the potential genetic conditions or birth defects that could affect the fetus.

For example, unlike the amniocentesis test, a CVS cannot detect open spina bifida (a birth defect involving the spine). CVS primarily focuses on detecting certain genetic conditions.

In some cases, CVS may need to be repeated if not enough fluid was collected or if there was difficulty interpreting the results. This does not mean there is a problem with your pregnancy.