Chorionic villus sampling (CVS)
Chorionic villus
sampling, often referred to as CVS, is a diagnostic test to detect chromosomal
abnormalities and other hereditary disorders. This test may be recommended by
your doctor if you or your partner has a family history of illness that
indicates potential risks.
How is CVS performed?
A CVS is a diagnostic
procedure in which certain chorionic villus cells are removed from the placenta
where they attach to the uterine wall.
There are two ways to
collect samples:
- Transcervical: An ultrasound guides a thin catheter through the cervix
to the placenta. The chorionic villus cells are gently drawn into the catheter.
This is the most common method.
- Transabdominal: Ultrasound guides a long, thin needle through the
abdomen to the placenta. The needle grasps the tissue sample and then
withdraws. This procedure is similar to amniocentesis.
The CVS procedure
allows larger samples to be collected and provides faster results than
amniocentesis. Results can be obtained from one to seven days.
When is CVS performed?
A CVS is usually
performed between 10 and 13 weeks after the last menstrual period. CVS may be
preferable to amniocentesis because it can be performed earlier in pregnancy.
What does a CVS test look for?
The study of
chorionic villi reveals chromosomal abnormalities (Down's syndrome) and genetic
disorders. This test differs from amniocentesis in that it does not check for
neural tube defects.
CVS also provides
access to DNA for prenatal paternity testing. DNA is taken from the potential
father and compared with DNA obtained from the child during a CVS. The results
are accurate (99%) in determining paternity.
What do CVS results mean?
CVS is a diagnostic
test that detects chromosomal abnormalities and genetic disorders with high
accuracy (98-99%). Although the probability of identification is high, this
test does not measure the severity of these disorders. This test does not
detect neural tube defects.
What are the risks and side effects for the mother or baby?
Although CVS is
considered a safe procedure, it is recognized as an invasive diagnostic test
with potential risks. Miscarriage is the main risk associated with CVS,
occurring in 1 in 100 procedures.
CVS is not
recommended for women who:
- Have an active infection
- Are carrying twins
- Have experienced vaginal bleeding during pregnancy
Transcervical CVS is
not recommended for women who:
- Have uterine fibroids
- Have a tilted uterus which impedes the catheter
After the procedure,
the mother may experience one or more of the following side effects:
- Infection
- Spotting
- Cramping and pain at the puncture point
- Contact your doctor if these symptoms remain or get worse.
You should also see
your doctor if you experience:
- Fever
- Chills
- Leaking of amniotic fluid
The probability of
getting a false positive result is 1%. A false positive result occurs when the
test shows that the fetus has an abnormality, but it does not.
What are the reasons to test or not to test?
Reasons for testing
or not testing vary from person to person and couple to couple.
Performing tests and
confirming the diagnosis gives you certain options:
- Pursue potential interventions that may exist
- Begin planning for a child with special needs
- Start addressing anticipated lifestyle changes
- Identify support groups and resources
- Make a decision about carrying the child to term
Some individuals or
couples may refuse to be tested or additional tested for a number of reasons:
- They are satisfied with the results, regardless of the outcome
- For personal, moral or religious reasons, deciding to carry a child to term is not an option.
- Some parents choose not to allow tests that could harm a developing child.