During your pregnancy, your healthcare provider may recommend some diagnostic tests as part of your prenatal care. These diagnostic tests are often done as a follow-up after a screening test. One of these diagnostic tests is called chorionic villus sampling. This test can help your provider diagnose or rule out your baby being born with a certain genetic disorder.

We’ve compiled some frequently asked questions about chorionic villus sampling so that you can find out more about how the test is done, and what exactly the test can detect.

What Is Chorionic Villus Sampling?

Chorionic villus sampling (CVS) is a type of prenatal diagnostic test in which cells from the placenta are examined in order to diagnose certain genetic disorders.

When Is Chorionic Villus Sampling Done?

Your healthcare provider may recommend CVS based on the results of earlier screening tests. If you choose to have this diagnostic test, it will generally be done in your first trimester, between 10 and 13 weeks of your pregnancy.

What Can Chorionic Villus Sampling Detect?

Chorionic villus sampling can detect genetic disorders such as Down syndrome, Tay-Sachs disease, sickle cell disease, fragile X syndrome, and cystic fibrosis. However, CVS does not detect birth defects like spina bifida.

To screen for certain other conditions like spina bifida, your healthcare provider may recommend tests such as a maternal serum alpha-fetoprotein screening test (a blood test performed in the second trimester) as part of your prenatal care.

Why Might Your Healthcare Provider Recommend Chorionic Villus Sampling?

Your healthcare provider might recommend chorionic villus sampling if:

  • Certain prenatal screening tests have come back positive

  • You had a previous pregnancy with a chromosomal condition

  • You are 35 or older, as this may mean your baby is at a higher risk of a chromosomal condition

  • You or your partner has a family history of a genetic disorder.

Chorionic villus sampling is an optional diagnostic test. Discuss your preferences with your healthcare provider so you can make an informed decision about what is right for you.

How Is a Chorionic Villus Sampling Test Done?

The CVS procedure involves taking a small sample of tissue (chorionic villi) from the placenta. The placenta contains the same genetic makeup as your baby. CVS is done in one of two ways:

  1. Transcervical CVS. A small tube is placed through the vagina and cervix in order to reach the placenta.

  2. Transabdominal CVS. A thin needle goes into the abdomen and the uterine wall in order to reach the placenta.

Before beginning the procedure, your healthcare provider will likely perform an ultrasound to determine your baby’s gestational age and the position of the placenta. The ultrasound can also help guide your provider while performing the CVS.

What Is the Difference Between Amniocentesis and Chorionic Villus Sampling?

Amniocentesis is a diagnostic test that is performed between 15 and 20 weeks of pregnancy, and it analyzes a sample of the amniotic fluid.

CVS, which takes a sample of cells from your placenta, is performed earlier than amniocentesis, usually in the first trimester.

Although CVS can be performed sooner, it isn’t as commonly performed as amniocentesis, and it may not be available in all medical centers. Talk to your healthcare provider if you have any questions about either diagnostic test.

What Are the Risks Associated With Chorionic Villus Sampling?

Although rare, the possible risks of CVS are:

  • An increased chance of birth defects if the test is done before 10 weeks

  • A very small risk (0.22 percent) of miscarriage.

After the procedure, your healthcare provider will make sure your baby is doing just fine by checking her heartbeat.

Most moms-to-be find CVS a painless procedure; however, some side effects and complications can occur, which may include:

  • Bleeding or spotting

  • Leakage of amniotic fluid

  • Infection

  • Fever

  • Contractions.

Contact your healthcare provider if you experience any of these symptoms. After the procedure, you should plan to rest.

Can the Results Be Wrong?

There’s a small chance you may receive a false positive result, which means the test came back positive but the medical condition doesn’t actually exist. If your healthcare provider suspects this is the case, she may recommend amniocentesis to help get clarity on the results.

Prenatal diagnostic tests can help confirm or rule out the results of an earlier screening test, and can provide you with more detailed information about your baby's health and well-being. Remember that these tests are optional; it’s your decision whether you want to have them or not. If you have any questions or concerns, turn to your healthcare provider, who can go over specific details with you.

How we wrote this article

The information in this article is based on the expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.