villus sampling or CVS is a diagnostic procedure performed
in the late first trimester or early second trimester that
involves obtaining a small tissue sample of chorionic villi
from the placenta.
are the indications for CVS testing?
CVS testing is most commonly performed for evaluation of
fetal karyotype (chromosomes) due to increased risk of fetal
chromosomal abnormalities associated with advanced
maternal age (AMA). Other indications include
- having a previous pregnancy
or child with a chromosomal abnormality,
- family history of chromosomal
- parental chromosomal abnormality,
- abnormal first trimester
screening for Down syndrome,
- family history of other
genetic disease / syndrome or inherited metabolic abnormality
for which prenatal diagnostic testing is available.
is CVS performed?
CVS procedures are generally performed between 10 and 13
weeks of gestation. In some circumstances it may be performed
as early as 9 weeks or as late as 14 weeks of gestation.
In pregnancies complicated by decreased amniotic fluid volume,
CVS may be performed at even later gestational ages.
is the CVS procedure performed?
Genetic counseling is provided prior to finalizing a decision
regarding early pregnancy testing by CVS.
- A detailed ultrasound
is performed for evaluation of fetal and maternal anatomy,
and careful evaluation of the placental implantation sight.
- The most common means
of obtaining chorionic villi by CVS is with a transvaginal
approach by insertion of a small flexible catheter into
the uterus through the cervix (with positioning that is
similar to undergoing a pap smear).
- CVS can also be performed
using a transabdominal approach for sampling chorionic
villi by insertion of a small needle into the lower abdomen
and uterus similar to the procedure performed for genetic
- A local anesthetic is
generally used for the transabdominal procedure. Both
techniques use ultrasound guidance for chorionic villi
- The tissue sample is
sent to a laboratory for evaluation of karyotype (chromosomes)
and any other indicated genetic testing.
are the CVS results available?
Final results of the chromosome testing following tissue
culture are generally received within 10-12 days of the
procedure. Results of testing for other genetic diseases
may take a longer period of time and generally are based
on the type of testing requested. In some cases preliminary
results may be obtained earlier following direct karyotyping
of uncultured chorionic villi (or trophoblasts), or using
a specialized laboratory technique such as fluorescent in
situ hybridization (FISH).
What are the advantages
of CVS testing as compared to amniocentesis?
The principle advantage of CVS testing is the availability
of early diagnostic testing. In general the results are
expected to be finalized in the late first or early second
trimester. With some genetic disorders early testing can
be important in determining duration of or need for continued
medical therapy. Receiving results earlier in pregnancy
also provides for greater patient privacy with regards to
decision-making when the test results are abnormal.
What are the risks
of CVS testing?
The procedure related pregnancy loss risk of CVS testing
is less than 1%. Chromosomal
mosaicism is found in approximately 1% of
CVS samples and generally requires follow-up amniocentesis
to confirm the presence or absence of mosaicism in the fetus.