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McKesson Clinical Reference Systems: Women's Health Advisor 2002.2
Chorionic Villus Sampling (CVS)
What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a procedure in which a
small sample of tissue is removed from the placenta early
in a pregnancy. The genetic information (chromosomes) in
this tissue is the same as the baby's. Genetic specialists
analyze the tissue. It can help them predict early in a
pregnancy whether the baby has a chromosome disorder, such
as Down syndrome.
CVS is a relatively new alternative to amniocentesis.
Amniocentesis is a procedure in which fluid is sampled from
the sac surrounding the baby. CVS can be done several weeks
earlier than amniocentesis. It is used to test for many of
the same disorders that amniocentesis tests for. Unlike
amniocentesis, however, CVS cannot detect neural tube or
spinal defects. A blood test (alpha-fetoprotein screening)
is recommended for this purpose at 15 to 18 weeks of
pregnancy.
When is it used?
You may consider having CVS because:
- You (the mother) will be 35 years old or older on the due
date.
- Your family or you have a history of a pregnancy or child
with a chromosome problem, such as Down syndrome or
birth defects.
- Your family has a history of mental retardation or
inherited disease such as Tay-Sachs, sickle cell anemia,
or cystic fibrosis.
- You have had two or more miscarriages.
- You have male relatives with diseases such as hemophilia
and muscular dystrophy.
How do I prepare for chorionic villus sampling?
CVS is performed early in pregnancy, usually 10 to 12 weeks
after the last menstrual period. To be sure CVS is done at
the right time, you should get a pregnancy test from your
health care provider as soon as you suspect you are
pregnant.
If you have had any spotting or bleeding, or if you are
unsure of the date of your last menstrual period, you
should have an ultrasound exam.
If you have a vaginal infection, it should be treated before
the test. For this reason, you health care provider will
get cultures of the cervix before the procedure. CVS can be
done if the cultures show that you do not have an infection.
What happens during the procedure?
CVS is performed either through the cervix (transcervical
CVS) or through the abdomen (transabdominal CVS). In the
transcervical procedure, a thin plastic tube is inserted
into the vagina and through the cervix to reach the
placenta. Ultrasound is used to help guide the tube. A
small sample of chorionic villus tissue is withdrawn.
In transabdominal CVS, a needle is inserted through the
abdomen and uterus and into the placenta. Ultrasound is
used to help guide the needle. A small amount of tissue is
withdrawn into a syringe. The procedure is similar to
amniocentesis.
What happens after the procedure?
Avoid strenuous activity for 1 to 2 days after the
procedure. You may have a small amount of bloody spotting
for up to a week, particularly if you had the transcervical
procedure.
Report any unusual symptoms or concerns to your health care
provider, such as:
- heavy bleeding
- contractions of the uterus or pain
- fever.
You may be able to have initial results within 3 to 4 days
of the test. You can usually expect a final result within
2 weeks.
What are the benefits of this procedure?
The main advantage of CVS is that it is performed earlier in
pregnancy than amniocentesis. Amniocentesis is usually done
during the 15th to 18th weeks of pregnancy. With CVS, you
can have the results of genetic tests before the 14th week
of pregnancy. This gives you more time to decide what
to do if your baby has chromosome problems. If you wish to
end the pregnancy, it is safer and easier at this time. It
may also be easier on you emotionally if the pregnancy is
ended early, before you start feeling the baby move.
Ending a pregnancy later may require induction of labor.
This is more difficult technically and may be more
emotionally distressing for you and your partner. If you
decide to continue the pregnancy, you have more time to
prepare for the baby's problems. You can find help from
health care providers, counselors, and parents of children
with similar problems.
What are the risks associated with this procedure?
The biggest risk is miscarriage after the procedure.
Miscarriages occur after CVS in about 1 of every 100
procedures. This is slightly higher than the risk with
amniocentesis, which is about 1 in 200 procedures.
Other problems that can occur from CVS are bleeding,
cramping, leaking of amniotic fluid, and infection. The
risk of these is rare, about 1% or less.
If CVS is done earlier than the 10th week after your last
menstrual period, there may be an increased risk that the
baby's jaw and limbs may not grow normally. Ask your health
care provider about this.
Rarely, it is not possible to get an accurate result from
CVS. In these cases, amniocentesis is usually recommended.
When should I call the health care provider?
Call your health care provider immediately if:
- You develop a fever.
- You have any change or worsening of pain or symptoms.
- You have any unusual or bloody drainage from the
vagina (more than small amounts of spotting).
Call your health care provider during office hours if:
- You have questions about the procedure or its result.
- You want to make another appointment.
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