Chorionic Villi Sampling (CVS)
The Center for Prenatal Diagnosis
Chorionic Villi Sampling (CVS)
Available testing
Chorionic villi sampling is a diagnostic procedure used
to test for certain genetic conditions. During CVS, a
small sample of the placenta is removed for laboratory
analysis. Depending on the location of the baby and the
placenta, the doctor will use one of the following two
approaches to obtain the sample:
Chromosome abnormalities
Chromosomes are the structures present in every cell
of our bodies that contain the genetic material that help
our body grow, develop, and function. Chromosomes are
the genetic material that we pass along to our children.
Normally, each cell contains 46 chromosomes. A missing
or extra chromosome causes changes in the way a baby
develops, and can lead to physical birth defects, mental
retardation, or both.
With the transcervical approach, ultrasound guidance is
used to insert a flexible catheter through the cervix.
With the transabdominal approach,
a thin needle is inserted through
the mother’s abdomen.
One of the most common chromosome abnormalities is
Down syndrome, caused by an extra copy of chromosome
21. People with Down syndrome have a characteristic
facial appearance, an increased risk for heart and bowel
defects and varying degrees of mental retardation.
Trisomies 13 and 18 are caused by an extra copy of
chromosome 13 and chromosome 18, respectively. Both
of these conditions are associated with severe birth
defects, mental retardation and a significantly shortened
lifespan.
Certain inherited genetic conditions
CVS can be used in a pregnancy known to have an
increased risk of inheriting certain genetic conditions.
Examples may include cystic fibrosis, sickle cell anemia,
Tay-Sachs, and others. Test results are available in
approximately 1-5 weeks.
The Center for Prenatal Diagnosis offers CVS between
10-12 weeks of pregnancy.
Results from CVS are typically available between 8-14
days after the procedure. In approximately 1 in 100, or
1%, of cases, results may be unclear. This may occur if
some of the mother’s cells are mixed with the placenta’s
cells, or if the placenta is made up of two or more
different types of cells. If this occurs, amniocentesis or
CVS may be required.
In a small number of cases, the CVS sample cannot be
used for testing. If this occurs, either a second CVS or
amniocentesis may be required.
What testing cannot be performed?
CVS cannot detect every genetic condition or abnormality.
With every pregnancy, there is a 3-5% chance of having a
baby with a birth defect, such as a heart defect, or mental
retardation.
Unlike amniocentesis, CVS cannot be used to detect open
neural tube defects (an opening in the baby’s spine).
It is recommended that women who choose to have CVS
receive an extensive ultrasound between 18-20 weeks
of pregnancy to screen for open neural tube defects.
An extensive ultrasound will detect greater than 95% of
open neural tube defects.
Detection rates
CVS will detect greater than 99% of chromosome
abnormalities. CVS does not detect open neural tube
defects.
What are the risks associated with CVS?
Miscarriage
The risk of miscarriage associated with the procedure is
estimated to be less than 1 in 125, or 0.8%.
Recent data supported by the American College of
Obstetricians and Gynecologists has indicated the rate of
miscarriage may be significantly less.
Bleeding/significant cramping/leakage of fluid
These symptoms are relatively common following a
CVS, but do not usually result in a miscarriage. If you
experience any of these symptoms, contact the Center
for Prenatal Diagnosis or your doctor.
Infection
Infection is very rare following CVS. However, if you
develop a fever above 100o or any flu-like symptoms,
contact the Center for Prenatal Diagnosis or your doctor.
Harm to the fetus
The risk to the fetus is extremely low, since ultrasound
guidance is used throughout CVS. Certain studies
have shown that CVS can increase the risk of limb
abnormalities when performed before 10 weeks of
pregnancy. However, when CVS is performed between
10-12 weeks of pregnancy, there is no increased risk
of limb abnormalities.
Restrictions after the procedure
For the first 24-48 hours after CVS, women should
avoid lifting heavy objects, having sexual intercourse,
or strenuous exercise.
Who should be offered CVS?
Advanced maternal age
Every woman has a chance of having a child with a
chromosome abnormality, such as Down syndrome.
This risk gradually increases with age. In the United
States, all women who will be 35 years old or older at
delivery are routinely offered prenatal diagnostic testing,
such as CVS or amniocentesis.
Family history of a chromosome abnormality,
certain inherited genetic conditions
If a close relative is known to have any of these
conditions, the pregnancy may be at an increased
risk for that abnormality or condition.
Parents who are carriers of certain inherited
genetic conditions
If the parents of a baby are found to be carriers for an
inherited genetic condition, the pregnancy may be at
an increased risk for that condition. Not all inherited
conditions are detectable with CVS.
Women with an abnormal first trimester
maternal serum screen
Maternal serum screening is used to identify pregnancies
at an increased risk for chromosome abnormalities.
Serum screening is typically offered to pregnant women
of every age. Diagnostic testing will be offered to women
whose first trimester serum screening showed the
pregnancy had an increased risk for a chromosome
abnormality.
Rh-negative women
Women with an Rh-negative blood type will receive an
injection of Rh immune globulin after CVS in order to
help prevent Rh condition in the baby.
Contact information
www.genzymegenetics.com
Center for Prenatal Diagnosis
James Sumners, MD
Harold A. Bivins, Jr., MD
8081 Township Line Road, Suite 200
Indianapolis, Indiana 46260
317.415.8070
womens.stvincent.org
Genetic Counselors
Heather Marin, MS, LGC
Rachel Doyel, MS, LGC
Megan Tucker, MS, LGC
Note
All statistics, including detection rates, are specific to Genzyme
Genetics. These values may be different for other laboratories.