FAQ: Chorionic Villus Sampling (CVS)

What is chorionic villus sampling?

Like amniocentesis, chorionic villus sampling (CVS) can detect significant chromosome problems, such as Down syndrome, as well as small extra or missing pieces of chromosomes, called copy number variants. Both tests can identify genetic diseases like cystic fibrosis, Tay-Sachs disease and sickle cell disease in at-risk fetuses.

The main advantage of CVS over amniocentesis is that it is performed much earlier in pregnancy, at 10 to 13 weeks, rather than 15 to 20 weeks. A disadvantage is that neural tube defects, such as spina bifida, can't be detected. A mother's blood test, called alpha fetoprotein (AFP) screening, and an ultrasound can be performed later in the pregnancy to screen for neural tube defects.

Doctors, nurses and other members of the health care team at the UCSF Prenatal Diagnostic Center bring a wealth of expertise and experience, having performed more than 17,000 chorionic villus sampling procedures over the past 25 years.

What happens during the procedure?

Your complete visit to the Prenatal Diagnostic Center will take about two hours. First, you will meet with a genetic counselor who will assess your pregnancy history and family history, explain options for prenatal screening and testing, and answer any questions or address any concerns you may have.

Then, you will have an ultrasound to assess the location of the placenta and the term of the pregnancy. The CVS procedure is done under ultrasound guidance and takes about 10 minutes. It involves removing a tiny piece of tissue from the placenta. The tissue is obtained either by inserting a needle across the abdomen or with a catheter inserted through the cervix. Most women don't find the procedure painful, but there may be some cramping or minor discomfort.

The tissue is cultured and a karyotype analysis, an evaluation of the chromosomes, is performed. The results will be available in about two weeks.

Are there any risks associated with the test?

There is a small risk of miscarriage as a result of CVS. The miscarriage rate for procedures performed at UCSF Medical Center is about 1 in 350.

What does a positive result mean?

If you have a positive result, this means the test found a genetic abnormality. In these instances, you will have a chance to discuss the diagnosis and your options with an obstetrical geneticist and a genetic counselor from the UCSF Prenatal Diagnostic Center as well as your own doctor. Referrals and support information are available for all decisions.

Will my insurance cover the cost?

Most insurance plans cover CVS and other prenatal tests, especially for women over 35 years of age. You may need a referral from your primary care doctor or an authorization from your health plan to ensure insurance coverage. Our office staff is available to assist you with insurance questions.


Reviewed by health care specialists at UCSF Medical Center.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.