Chorionic villus sampling (CVS), sometimes called "chorionic ''villous'' sampling" (as "villous" is the adjectival form of the word "villus"), is a form of

prenatal diagnosis Prenatal testing is a tool that can be used to detect some birth defects at various stages prior to birth. Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problem ...

done to determine

chromosomal A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most importa ...

or genetic disorders in the

fetus A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

. It entails sampling of the chorionic villus (

placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...

l tissue) and testing it for chromosomal abnormalities, usually with

FISH A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

or PCR. CVS usually takes place at 10–12 weeks' gestation, earlier than

amniocentesis Amniocentesis is a medical procedure used primarily in the prenatal diagnosis of genetic conditions. It has other uses such as in the assessment of infection and fetal lung maturity. Prenatal diagnostic testing, which includes amniocentesis, is ...

or percutaneous umbilical cord blood sampling. It is the preferred technique before 15 weeks. CVS was performed for the first time in

Milan Milan ( , , ; ) is a city in northern Italy, regional capital of Lombardy, the largest city in Italy by urban area and the List of cities in Italy, second-most-populous city proper in Italy after Rome. The city proper has a population of nea ...

by Italian biologist Giuseppe Simoni, scientific director of Biocell Center, in 1983. Use as early as eight 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 Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

findings *Family history of a

chromosomal abnormality A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where ther ...

or other

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders ...

*Parents are known carriers for a

* Advanced maternal age (maternal age above 35). AMA is associated with increase risk of Down's syndrome and at age 35, risk is 1:400. Screening tests are usually carried out first before deciding if CVS should be done.

Risks

The risk of miscarriage in CVS is estimated to be potentially as high as 1–2%. However some recent research has suggested that only a very small number of miscarriages that occur after CVS are a direct result of the procedure. Apart from a risk of miscarriage, there is a risk of infection and

amniotic fluid The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...

leakage. The resulting amniotic fluid leak can develop into a condition known as

oligohydramnios Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. The limiting case is anhydramnios, where there is a complete absence of ...

, 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 (underdeveloped 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 Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgi ...

follows 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 Mesenchymal stem cells (MSCs), also known as mesenchymal stromal cells or medicinal signaling cells, are multipotent stromal cells that can differentiate into a variety of cell types, including osteoblasts (bone cells), chondrocytes (cartilage ...

. 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 (1-2%) of pregnancies have confined placental mosaicism, where some but not all of the

l cells tested in the CVS are abnormal, even though the pregnancy is unaffected. Cells from the mother can be mixed with the

l cells obtained from the CVS procedure. Occasionally if these maternal cells are not completely separated from the

l sample, this can lead to discrepancies with the results. This phenomenon is called Maternal Cell Contamination (MCC). 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.

References

External links

Chorionic Villus Sampling - March of Dimes
*
Cleveland Clinic

CVS Test: Six Months of Worry Free Pregnancy

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