An Introduction to Chorionic Villus Sampling

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Chorionic villus sampling (CVS) is a prenatal test in which a biopsy of the placenta is obtained vaginally or abdominally at 10-13 weeks gestation for genetic testing. CVS can tell the genetic sex of the fetus and if the fetus has inherited the genetic condition being tested for. Genetic testing that is done by CVS include a karyotype, fluorescent in situ hybridization (FISH), chromosomal microarray and testing for a specific genetic condition.

  • Karyotype: Shows a picture of the chromosomes in a single cell, which allows identification of a chromosome condition such as Down syndrome, as well as the predicted genetic sex of the fetus.
  • FISH: Applies dye that attaches to certain chromosomes, also allowing the patient to know the predicted genetic sex of the baby, and also how many copies of chromosomes 21, 18, 13, X and Y are present.
  • Microarray: More detailed molecular karyotype, which tells you how many copies of each chromosome there are, and whether or not those chromosomes have any deletions or extra pieces, and also reports the predicted genetic sex of the fetus.
  • Analysis for specific genetic conditions takes about 1-3 weeks and requires a maternal blood sample in addition to the fetal sample.

CVS is the earliest test (first trimester) for genetic testing that you can do in pregnancy. However, there are some risks, such as there being an approximate 0.3-0.5% chance of miscarriage. Additionally, about 1% of the chromosome results are mosaic, meaning that there can be a chromosomal abnormality present in the placenta that is not present in the fetus. If this is the case, an amniocentesis is recommended.

Finally, if maternity coverage is covered by your health insurance, both the chorionic villus sampling and genetic testing are likely to be covered benefits(although, the genetic testing may require pre-authorizations). If it is not a covered benefit, these tests can be costly in the United States: $1,000 for a karyotype, $1,200 for a FISH, $3,000 for a microarray, and about $500-$2,000 for genetic testing for a genetic condition. In countries with nationalized healthcare, such as the United Kingdom, CVS may be covered.

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This project is sponsored by Myriad Genetics.

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