Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is a test done during early pregnancy that can find
certain problems with your
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)
No abnormalities are found in
the genetic material of the chorionic villus cells.
Abnormalities are found in the
genetic material of the chorionic villus cells.
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
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
- 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.
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.