Chorionic Villi Sampling (CVS)
If you are considering whether to have chorionic villus sampling (also called CVS), you also first read the
article about amniocentesis. Amniocentesis and chorionic villus sampling are two different options for
having genetic testing of a pregnancy. If you are trying to decide whether to have a test or which of these
two tests to have, the information in this article is intended to supplement the information provided in the
article regarding amniocentesis.
CVS can be performed by inserting a needle through the abdomen into the uterus (transabdominal) or by
inserting a plastic catheter into the uterus through the cervix (transcervical). We usually prefer to use the
transabdominal CVS method. With this method a needle is placed into the uterus through the lower
abdomen. For the woman, this procedure is very similar to amniocentesis. The needle is the same thickness
as that used to draw blood from your arm but is somewhat longer. With the transcervical approach, a
speculum is placed in the vaginal and a plastic catheter is inserted into the opening of the cervix and into the
uterus. The needle or catheter is passed into the developing placenta. During the entire procedure, the
position of the needle or catheter is observed and guided by ultrasound. Once the needle or catheter is
properly positioned, small fragments of the developing placenta are drawn up the needle or catheter with a
syringe. The sample is immediately examined to determine if enough cells have been obtained to perform
test. In most cases, the number of cells obtained will be sufficient to complete the test. If CVS is
unsuccessful after three attempts, we recommend stopping the procedure and waiting until an
amniocentesis can be performed.
As with amniocentesis, there is concern that having the test may cause a woman to miscarry. The likelihood
of having a miscarriage due to CVS is not known with certainty. About 4% of women who have had CVS
have had a miscarriage following the test. We do not know which of the miscarriages are actually due to the
test, although it is believed that many of them are not due to the test but would occur spontaneously, even
without the test. Several studies suggest that CVS has about a 0.5-1.0% greater risk than amniocentesis for
causing a miscarriage. For some patients having the test done during the first three months of pregnancy,
and knowing the results quickly is considered such an advantage, that they are willing to assume a slightly
higher risk rather than wait for amniocentesis.
There is also a small but important risk of infection in the uterus following CVS. Because this is rare, the
exact frequency of infection occurring has not been accurately determined. We believe that when we use the
transabdominal method for CVS, the frequency of this complication is very rare and may be the same as
with amniocentesis.. Although a rare complication of CVS, infections in the uterus during pregnancy can
progress rapidly and become very serious. Very rare cases of shock and even death have been reported
when the uterus and pregnancy become infected. In addition to antibiotics, termination of the pregnancy if
often necessary to effectively treat these infections before serious complications occur. Following your CVS,
you will be given an instruction sheet about how to watch for infection and other complications of the test
It may be possible for the needle or catheter used for CVS to penetrate the membranes or sac of fluid
around the fetus. If this happens, there is a possibility of injury to the fetus. Because this is also so rare, we
do not know the exact frequency of complications resulting from entering the sac. If this complication occurs,
the doctors will discuss any concerns with you.
It is also possible for an Rh-negative woman to develop an Rh problem due to CVS. This can effectively be
prevented by giving these women a small dose of Rh immune globulin (RhoGam) immediately after the test
if they are Rh-negative. The administration of RhoGam is standard treatment for Rh-negative women who
have amniocentesis or following delivery of a baby.
When CVS was first introduced as a test, there was a concern that removal of even a few small fragments of
the placenta could lead to problems with the normal growth of the fetus or the function of the placenta later
in the pregnancy. Problems with growth of the fetus or function of the placenta have not been observed with
any greater frequency in women who have had CVS. It has also been suggested that CVS may actually
cause certain birth defects. After reports of children born with missing fingers and toes and/or
underdevelopment of the lower jaw following CVS there was publicity about this risk of the test. Many of
these women had CVS at a very early time in pregnancy (6-10 weeks). This led to the recommendation to
wait until the end of the first three months of pregnancy to perform CVS. Whether CVS causes these
problems when it is done at this later time remains controversial. Whether the few cases reported were
naturally occurring or associated with the procedure is still debated. At worst, it seems that the risk of a
defect being caused by CVS is in the range of 1 in 3,000 pregnancies in which the test is performed.
With amniocentesis you will have testing for spina bifida even though you may not have a special risk for this
problem. This defect occurs in about 1 out of 1,000 newborns and is usually associated with significant
handicaps. Following CVS, we suggest that you consider having a blood test for spina bifida at 16 weeks of
pregnancy. An ultrasound to evaluate the fetal anatomy at about 20 weeks of pregnancy will also be
recommended The combination of the blood test and the ultrasound will detect more than 90% of spina
bifida.
The accuracy of CVS testing for detection of Down syndrome is comparable to the accuracy of
amniocentesis. The analysis of the structure of the individual chromosomes is not quite as detailed with CVS
as it is with amniocentesis. Therefore, if you have a special risk for a problem that may require detailed
analysis of the structure of a particular chromosome, we may recommend amniocentesis. For most patients,
we feel that CVS offers as reliable a test as amniocentesis. Except for spina bifida, almost all of the
disorders that can be detected by amniocentesis can also be detected by CVS. As with amniocentesis, only
a limited number of tests can be performed on a single sample. This means that other genetic diseases or
birth defects can be present but a test was not performed for that problem.. Also, many genetic diseases or
birth defects cannot be detected by CVS or amniocentesis. Therefore, no combination of tests can
guarantee a normal baby.
We are able to obtain a sample and complete our studies in the majority of women having the test, but the
success rate with CVS is slightly lower than it is with amniocentesis. If the procedure or laboratory testing is
unsuccessful, you will be offered an amniocentesis rather than a repeat CVS..
In the past, we occasionally experienced unexpected or confusing results with amniocentesis. Now we have
many thousands of cases and many years of experience to help us interpret these results. At times, we may
find confusing results with CVS. If this occurs, we may recommend delaying a decision about terminating the
pregnancy and checking the results by performing an amniocentesis. Overall, about 1% of women who have
CVS also have amniocentesis. Reasons for this include: an unsuccessful CVS, failure to obtain the
laboratory result, or confusing laboratory results.
The major advantage of CVS is that a woman can learn very early in a pregnancy, if the fetus has a
particular problem. If she decides to terminate the pregnancy, this can be done before the pregnancy is
noticeable to other people and before the mother feels the baby moving. Termination of the pregnancy
during these early weeks of pregnancy is easier and slightly safer for the woman than it is at a later point in
the pregnancy. For these reasons, women who have a high chance of an abnormal test result or who want
early results for other reasons may plan to have CVS.. Nevertheless, you should not have CVS without also
reading information about amniocentesis and considering both options carefully.
Michael M. Mennuti, M.D.