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Chorionic Villi Sampling

PD_ Fitness and WellBeing_67058Chorionic villi sampling (CVS) is a test in early pregnancy. It is done to look for signs of birth defects. Cells from parts of the placenta are taken. Genetic material from the fetus can be found there.

The test may provide important information. However, there are some risks. You and your doctor should discuss the risks and benefits.

Who Should Have CVS?

Some birth defects may change the course of pregnancy or prenatal care. If you are at higher risk for having a baby with birth defects, you may wish to have this test. Examples of things that may put you at higher risk are:

  • Age 35 years old or older when you give birth
  • Family history of certain birth defects
  • Previous child with a birth defect
  • Abnormal results on other genetic screening tests

Understanding the Procedure

CVS is usually done about 10-12 weeks after a woman's last menstrual period. It is done after a pregnancy is confirmed. The procedure may be done in the doctor's office or hospital. The sample can be collected two ways. Through the vagina is a common option. However, that may not be possible if there are problems in the cervix, bleeding, or a sexually passed infection. In this case, CVS may be done through the belly.

An ultrasound examwill be done to see the position of the placenta. It will also help guide the doctor during the test. Results may take up to 2 weeks.

For a vaginal procedure, a tube will be passed through the vagina into the cervix. The tube will be passed to the placenta where a sample will be removed.

For procedure through the belly, a needle will be used. The needle will be passed through the belly into the uterus and placenta. A small sample will be drawn out through the needle.

Results may take up to 2 weeks.

Risks of Having CVS

There are some risks to consider before taking this test. The use of the needle or the tube may lead to an infection. Women who have CVS also have a slightly higher risk of miscarriage. It can also cause some cramping or bleeding.

If you have a higher risk of birth defect, or you have other concerns about prenatal testing, talk to your doctor.

CVS cannot detect a certain type of defect called open neural tube defects. If you have CVS, you will want to consider having a blood alpha-fetoprotein (AFP) test later in your pregnancy. This can show presence of neural tube defects.


International Childbirth Education Association

The American Congress of Obstetricians and Gynecologists


Health Canada

Women's Health Matters


Chorionic villus sampling: CVS. American Pregnancy Association website. Available at: http://americanpregnancy.org/prenatal-testing/chorionic-villus-sampling. Updated September 2, 2016. Accessed October 24, 2016.

Prenatal care and tests. Office on Women's Health website. Available at: https://www.womenshealth.gov/pregnancy/you-are-pregnant/prenatal-care-tests.html. Updated September 27, 2010. Accessed October 24, 2016.

Prenatal diagnosis: Amniocentesis and CVS. Family Doctor—American Academy of Family Physicians website. Available at: http://familydoctor.org/familydoctor/en/pregnancy-newborns/fetal-health/prenatal-diagnosis-amniocentesis-and-cvs.html. Updated August 2010. Accessed October 24, 2016.

Routine prenatal care. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T114252/Routine-prenatal-care. Updated June 22, 2016. Accessed October 24, 2016.

Last reviewed August 2018 by Monica Zangwill, MD, MPH  Last Updated: 9/13/2018