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Chorionic Villus Sampling: Prenatal Genetic Testing

CVS can detect Down syndrome and other chromosome and genetic problems in the first trimester. Find out when and how this test is used.

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Chorionic villus sampling (CVS) is a prenatal test. It checks for chromosomal or genetic birth defects in your baby. To do the test, your doctor inserts either a small tube through your vagina and cervix, or a thin needle through your abdomen and uterus. Your doctor then takes a tiny piece of tissue from the placenta without touching the baby. This tissue, called chorionic villi, contains the same chromosomes as your baby.

Test results usually are complete within 10 days.

Why would I have CVS?

A CVS test is often offered if you had an abnormal result on a first trimester screening test. It is also suggested if you are at risk for a baby with chromosomal or genetic birth defects. It is done between 10 and 13 weeks of pregnancy.

You may be at risk for having a baby with chromosomal or genetic birth defects if you:

  • Are 35 or older. The older you are, the higher your risk of having a baby with Down syndrome and other genetic defects.
  • Already have a biological child with a chromosome defect.
  • Have a family member with or personal history of inherited genetic disorders that CVS can identify. The test can detect about 200 disorders including Tay-Sachs disease, sickle cell disease and cystic fibrosis.
  • Have abnormal results from screening tests, such as a fetal ultrasound exam.

You may want to consider genetic counseling, especially if you have any risk factors for genetic or chromosomal abnormalities. A genetic counselor can help you understand your risks. He or she can also help you choose if having the tests is right for you.

What are the risks of CVS?

Cramping and spotting are common for the first day or so after the test. Call your doctor if you have a fever or heavy bleeding, or any symptoms that worry you.

CVS does have a small risk of miscarriage. Talk to your doctor, as she can give you the most current information regarding the risk of miscarriage for your situation.

Is there another test that gives the same information?

Both CVS and amniocentesis are invasive tests with a small risk of miscarriage and other complications. Your doctor can help you weigh the risks and decide which test might be best for you.

Amniocentesis can give similar results. But it is done later in your pregnancy than CVS. You may want these results sooner. And CVS does not screen for neural tube defects involving the baby. These occur when the spine doesn’t close as it should.  Women who choose CVS can have a blood test in the second trimester to check for neural tube defects.

By Susan Warner, Contributing Writer

American College of Obstetricians and Gynecologists (ACOG). Chapter 25: Screening and diagnostic testing for genetic disorders. In: ACOG’s Your Pregnancy and Childbirth: Month to Month. 6th edition. Washington, D.C.: ACOG; 2015.
The American College of Obstetricians and Gynecologists. Screening for birth defects. Accessed: July 13, 2016.
National Institutes of Health (NIH). National Human Genome Research Institute. Chromosome. Accessed: July 13, 2016.
March of Dimes. Chorionic villus sampling (CVS). Accessed: July 13, 2016.

Last Updated: July 14, 2016