What is chorionic villus sampling?
villus sampling (CVS) is a test that can find certain problems with a
fetus. CVS is done late in the first trimester, most
often between the 10th and 12th weeks.
CVS can find:
- Chromosomal birth defects, such as Down
- Hundreds of inherited diseases, such as
Tay-Sachs disease and
CVS cannot find neural tube defects, such as spina
bifida, so a blood test (alpha-fetoprotein test) is recommended along with it.
This blood test is usually done between the 16th and 18th weeks of
Should I consider CVS?
CVS may be a good choice
for you if:
- You have had a screening test in the first trimester that
suggests that your fetus may have Down syndrome. (This is an ultrasound of the
fetus's neck [nuchal translucency] and a test of your blood.)
are 35 or older. At 35, your risk of having a child with Down syndrome is high
enough that you may want to think about testing, and the risk increases as you
age. In mothers who are 35, about 1 baby in 350 is born with Down syndrome. By
age 40, about 1 baby in 100 is born with Down syndrome.1
- Either or both parents could pass on a disease
that runs in the family (genetic disorder), such as Tay-Sachs
disease or sickle cell disease, or a
- You have a medical
reason to need to know whether the fetus is male or female. This is important
when a parent is a
carrier of a sex-specific disease, like hemophilia or
Duchenne muscular dystrophy. Both of these diseases
occur mainly in males.
- You already have a child who has Down
syndrome or another chromosome defect.
ultrasound suggested that the fetus may have a birth
CVS may be expensive, and it is not available in all
areas. Most insurance companies will cover the cost for women older than 35.
But if cost or availability is an issue, you may decide to choose another type
How is CVS done?
During CVS, a sample of chorionic
villus cells is taken and checked for problems. Chorionic villi are tiny
fingerlike growths in the
placenta. The genetic material in these cells is the
same as that in the fetus's cells.
The doctor can collect the
sample in one of two ways:
- Put a thin flexible tube (catheter) through
the vagina and cervix into the placenta. This is called transcervical
- Put a long, thin needle through the belly into the placenta.
This is called transabdominal CVS. It is similar to the way amniocentesis is
The doctor uses ultrasound to guide the catheter or
needle to the right spot.
How would I use the results from CVS?
results from CVS suggest that a fetus does not have a chromosome or
gene defect. This can be reassuring. But it is
important to remember that no test can rule out all problems or guarantee that
your baby will be healthy and free of birth defects.
If the test
shows that your fetus has a disease or birth defect, you can make informed, if
hard, decisions. Your choices will depend on many things. These include the
type of defect involved and your feelings. For example, you may want to think
- Whether to continue the pregnancy. If a
fetus has a severe defect, some women choose to end the pregnancy, which is
safest and easiest in the first trimester. Others use the time to learn about
caring for and raising a child who has a birth defect or disease.
Where to have the baby. If the fetus has a serious problem, it is best to
deliver at a hospital with a neonatal intensive care unit (NICU) that offers
special care for newborns.
- Whether to have a vaginal delivery or
to plan a
C-section, based on the fetus's problem.
What are the risks of CVS?
CVS increases the
- Infection in the uterus.
- Miscarriage. In one recent study of highly trained providers, about 1
woman in 400 who have CVS had a 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.
There is a very small chance of CVS causing bleeding,
which could mix your blood and your fetus's blood. If you have Rh-negative
blood, you will be given a vaccine before the test to prevent
What are the risks of not having CVS if it is recommended?
If you don't have CVS or other prenatal testing and
the baby has a disease or birth defect:
- The birth could be harder and more risky for
the baby if the doctor doesn't know about the problem ahead of time.
- You could give birth in a hospital that doesn't have a neonatal
intensive care unit for sick newborns.
- You may not be emotionally
ready for a baby who is sick or has a birth defect.
Talk to your doctor about all of your testing options.
You may be able to rule out a genetic condition with another type of
Is there another test I can have instead of CVS?
You could also consider
amniocentesis, which is done in the second trimester.
Amniocentesis can detect more than 100 inherited diseases and Down syndrome, as
well as neural tube defects.
For this test, the doctor inserts a
needle through your belly into the uterus and draws out a small amount of
amniotic fluid. To look for genetic information, amniocentesis is done between
the 15th and 20th weeks of pregnancy, when there is enough amniotic fluid for
To compare these two tests:
- CVS can be done earlier in pregnancy than
amniocentesis, which gives you more time to make decisions and less time to
worry. If you would end the pregnancy based on test results, this would be
safest and easiest in the first trimester.
- CVS does not test for neural tube defects. If you have CVS,
you can have a blood test in the second trimester to find out if you are at
increased risk of neural tube defects. If the blood test suggests a problem, it
is followed by an ultrasound of the fetus.
- Results of CVS are
ready within 1 week. It can take from 2 weeks to 1 month to get the results of
- When done by highly trained providers, both tests
have about the same risks of miscarriage. In a study of highly trained
providers, the risk from amniocentesis and from CVS was about 1 in 400.2 Other studies have shown higher risks, between 2 and 4 in
400.3 This greater risk may be more likely in medical
centers with less experienced providers, especially for CVS.
is not available in all areas. It requires more training and is harder to do
If you need more information on prenatal testing, see
the medical tests:
- Chorionic Villus Sampling.
- Fetal Ultrasound.
- Alpha-Fetoprotein in Blood.