Chorionic villus sampling, sometimes called "chorionic villous sampling", is
a form of prenatal diagnosis to determine chromosomal or genetic
disorders in the fetus. It entails sampling of the chorionic villus and
testing it for chromosomal abnormalities, usually with FISH or PCR.
CVS usually takes place at 10–12 weeks' gestation, earlier than amniocentesis or
percutaneous umbilical cord blood sampling. It is the preferred technique
before 15 weeks. CVS was performed for the first time by
Italian biologist Giuseppe Simoni, scientific director of Biocell Center,
in 1983. Use as early as 8 weeks in special
circumstances has been described. It can be performed in a transcervical
or transabdominal manner. Although this procedure is mostly
associated with testing for Down Syndrome, overall, CVS can detect more
than 200 disorders. Indications
Possible reasons for having a CVS can include:
Abnormal first trimester screen results Increased nuchal translucency or other
abnormal ultrasound findings Family history of a chromosomal
abnormality or other genetic disorder Parents are known carriers for a genetic
disorder Advanced maternal age. AMA is associated
with increase risk of Down's syndrome and at age 35, risk is 1:400. Screening
test are usually carried out first before deciding if CVS should be done.
Risks Risk of miscarriage in CVS is about 0.5
- 1%. Apart from a risk of miscarriage, there is a risk of infection and
amniotic fluid leakage. The resulting amniotic fluid leak can develop into a
condition known as oligohydramnios, which is low amniotic fluid level. If
the resulting oligohydramnios is not treated and the amniotic fluid continues
to leak it can result in the baby developing hypoplastic lungs.
Additionally, there is also mild risk of Limb Reduction Defects associated with
CVS, with the risk being higher the earlier the procedure is carried.
It is important after having CVS that the obstetrician follow the patient
closely to ensure the patient does not develop infection.
Chorionic villi and stem cells Recent studies have discovered that
chorionic villi can be a rich source of fetal stem cells, multipotent
mesenchymal stem cells A potential benefit of using fetal stem
cells over those obtained from embryos is that they side-step ethical concerns
among anti-abortion activists by obtaining pluripotent lines of
undifferentiated cells without harm to a fetus or destruction of an embryo. These
stem cells would also, if used to treat the same individual they came from,
sidestep the donor/recipient issue which has so far stymied all attempts to use
donor-derived stem cells in therapies. Artificial heart valves, working
tracheas, as well as muscle, fat, bone, heart, neural and liver cells have all
been engineered through use of fetal stem cells
The first fetal stem cells bank in US is active in Boston, Massachusetts.
Limitations A small percentage of pregnancies have
confined placental mosaicism, where some but not all of the placental cells
tested in the CVS are abnormal, even though the pregnancy is unaffected.
Cells from the mother can be mixed with the placental cells obtained from the
CVS procedure. Occasionally if these maternal cells are not completely
separated from the placental sample, this can lead to discrepancies with the
results. This phenomenon is called Maternal Cell Contamination. CVS cannot
detect all birth defects. It is used for testing chromosomal abnormalities or
other specific genetic disorders only if there is family history or other reason
to test. See also
Amniocentesis Percutaneous umbilical cord blood
sampling Prenatal diagnosis
References External links
Chorionic Villus Sampling - March of Dimes
MedlinePlus Encyclopedia 003406 Cleveland Clinic
CVS Test: Six Months of Worry Free Pregnancy
Chorionic Villus Sampling - slideshow by The New York Times