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Health & Pregnancy

Pregnancy Essentials

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Chorionic Villus Sampling (CVS)

(continued)

Results

Chorionic villus sampling (CVS) is a test done during early pregnancy that can find certain problems with your baby (fetus).

Cells from your baby are looked at carefully for the proper number and arrangement of the genetic material (chromosomes) that show genetic diseases. Normally there are 46 chromosomes in each cell, arranged in 23 pairs. Chromosomes also tell the sex of your baby. It may take 1 to 2 weeks to get CVS results.

**Chorionic villus sampling (CVS)**
Normal:	No abnormalities are found in the genetic material of the chorionic villus cells.
Abnormal:	Abnormalities are found in the genetic material of the chorionic villus cells.

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What Affects the Test

In rare cases, the chorionic villus cells may have abnormal genetic material even though the baby's cells are normal. This is called a false-positive result. An abnormal test result may need to be confirmed by amniocentesis.

What To Think About

Normal results from chorionic villus sampling (CVS) do not guarantee that your baby will be healthy. CVS cannot find neural tube defects.
Amniocentesis (which is usually done later in the pregnancy than CVS) can also be used to find other diseases of the fetus, such as neural tube defects. If CVS does not show clear results, amniocentesis may need to be done.
In one study of highly trained providers, both CVS and amniocentesis had about a 1-in-400 chance of miscarriage.² Some studies have shown a slightly higher risk, from 2 to 4 in 400.³ This greater risk may be more likely in medical centers with less experienced providers, especially for CVS. For more information, see the topic Amniocentesis.
CVS is done if you are at high risk for having a baby with a chromosomal birth defect (such as Down syndrome) or a family genetic disease (such as Tay-Sachs disease or hemophilia). The benefits of this test often outweigh the risks. Genetic diseases and birth defects can be found earlier in pregnancy by CVS than by amniocentesis. This allows you to make an earlier decision whether to continue or end the pregnancy.
The results of CVS may vary depending on how the sample was taken.
If you have a vaginal infection (such as a vaginal yeast infection or genital herpes), a belly procedure will be used instead of a vaginal procedure.
CVS causes bleeding that could lead to mixing of your blood and your baby's about half of the time. If you have Rh-negative blood, you will be given the Rh immune globulin vaccine (such as RhoGAM) to prevent Rh sensitization which could harm your baby if he or she has Rh-positive blood.

Citations
Alfirevic Z, et al. (2003). Amniocentesis and chorionic villus sampling for prenatal diagnosis. Cochrane Database of Systematic Reviews (3).
Caughey AB, et al. (2006). Chorionic villus sampling compared with amniocentesis and the difference in the rate of pregnancy loss. Obstetrics and Gynecology, 108(3): 612-616.
Seeds JW (2004). Diagnostic mid trimester amniocentesis: How safe? American Journal of Obstetrics and Gynecology, 191: 608-616.
Other Works Consulted
American College of Obstetricians and Gynecologists (2007, reaffirmed 2008). Screening for fetal chromosomal abnormalities. ACOG Practice Bulletin No. 77. Obstetrics and Gynecology, 109(1): 217-227.
Cunningham FG, et al. (2010). Prenatal diagnosis and fetal therapy. In Williams Obstetrics, 23rd ed., pp. 287-311. New York: McGraw-Hill Medical.
Wapner RJ, et al. (2009). Prenatal diagnosis of congenital disorders. In RK Creasy et al., eds., Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice, 6th ed., pp. 221-274. Philadelphia: Saunders Elsevier.

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WebMD Medical Reference from Healthwise

Last Updated: May 06, 2010

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.