Chorionic Villus Sampling

Prenatal Genetic Testing

Beth Israel Deaconess Medical Center (BIDMC) provides comprehensive prenatal care for pregnant people and their babies. Our genetic counselors work with our maternal-fetal medicine specialists and clinical geneticists to offer you the most advanced genetic testing available.

Chorionic villus sampling (CVS) is an early prenatal genetic test that some pregnant patients choose to have between 10 and 13 weeks of pregnancy. If you’re considering CVS, you’ll meet with one of our genetic counselors prior to the test. The counselor will discuss the risks and benefits of the procedure, as well as gather your genetic family history.

What to Expect

The procedure uses ultrasound guidance. Our team can perform chorionic villus sampling (CVS) either vaginally or through the abdominal wall. In most cases, we perform CVS vaginally, but this depends on the location of the placenta.

During the procedure, the technician uses ultrasound to guide a thin needle or catheter to the area where the placenta is implanting. A syringe is attached to the back of the catheter for the technician to remove a small sample of tissue. The tissue sample is about 10 to 25 mg in size — about the size of a very small pea. The laboratory then cultures the tissue to analyze the chromosomes. Depending on the CVS test results, your prenatal care team may suggest further diagnostic tests for other genetic conditions.

For the procedure, we may ask that you have a full bladder. This allows us to better view the placenta with transabdominal ultrasound. There may be a bit of uterine pressure or cramping, but most patients have little discomfort. Occasionally, we may use a local anesthetic to numb the area.

After Chorionic Villus Sampling

After the procedure, we recommend that you limit your physical activities that day. Many patients can return to work the same day. It is normal to have a little cramping or bleeding, which should subside within 48 hours. If you have heavy bleeding, sharp cramps or flu-like symptoms, call your prenatal care team right away.

You typically receive your CVS results in 10 days. In some cases, results may take as long as two weeks. This will depend primarily on how well the cells grow in culture. Please know that the amount of time the lab needs to complete the chromosomal analysis doesn’t have anything to do with the health of the fetus.

Safety Concerns

There is a 1 in 400 (0.3%) risk of miscarriage associated with the CVS procedure. Also, a few scientific studies have raised concern about the incidence of certain types of birth defects in fetuses of patients who’ve had this procedure. We will discuss this risk factor with you at the time of counseling.

To address the possibility of risks to your offspring, we recommend that you contact one of our genetic counselors to review any family history concerns. It’s up to you to decide whether or not to consider prenatal diagnosis. It is important to remember that there is no one test or combination of tests that will rule out the presence of all fetal birth defects, chromosomal abnormalities or genetic disease.