Pregnancy Testing

Chorionic Villus Sampling

Chorionic Villus Sampling (CVS) is a genetic test that allows for earlier diagnosis and faster results than an amniocentesis. It can predict down syndrome, sickle cell anemia and any neural tube defects and is usually done between 10 and 12 weeks of gestation (12 and 14 weeks of pregnancy). The rates of complications for the baby are equal to those of amniocentesis during the second trimester.

The sample is chorionic tissue, which is part of the placenta. Because the baby and placenta both grow from the fertilized egg, the genetic material in the placenta is identical to your baby's. This allows accurate diagnosis of many genetic conditions.

What you need to know

There are two ways to perform the procedure. Both involve inserting a needle to collect the sample, but one method inserts the needle through your abdomen and the other inserts the needle through your cervix.

Most common risk is vaginal spotting. 0.3% of mothers miscarry after CVS, 0.1% have a rupture of the membranes and 0.5% get an infection in the placenta. Because there is a risk of placental bleeding, mothers who are Rh negative will need RhoGam to avoid additional complications.

CVS is a more difficult procedure to learn than amniocentesis, which may affect your access to this test.


Whether done through the abdomen or cervix, the procedure is done sterile to prevent infection. A needle is inserted and guided by use of ultrasound to the placenta. Once in the correct location, a sample is taken.


Nicolaides, K. (2005) First-trimester screening for chromosomal abnormalities. Seminars in Perinatology 29(4) 190-194.