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Test Code: CG CVS
General Information: CVS: Typically, CVS is performed during the first trimester of pregnancy at 10 to 12 weeks of gestation, while amniocentesis is performed during the second trimester at 14 to 18 weeks of gestation. Placental chorionic villi tissue, a fetal tissue of extra-embryonic origin, is obtained at 10 to 12 weeks of gestation by transcervical or transabdominal sampling. The sample is cleaned of obvious blood and maternally derived decidua tissue. The sample is then enzymatically disaggregated and placed in culture. These cultures can then be harvested for chromosomal analysis or grown for biochemical or molecular analysis. It should be noted that while the chromosomal complement is generally the same between the CVS and the fetus, in 1-2% of cases mosaic or non-mosaic chromosome anomalies can be observed in the CVS, but not recognized in the fetus. These anomalies may represent either confined placental mosaicism (CPM) or a true mosaicism of the fetus. Such findings make second trimester amniocentesis necessary.
  • Advanced maternal age (> 35 years of age at EDC)
  • Previous child/pregnancy with a chromosome abnormality
  • Family history of an inherited chromosome abnormality
  • Abnormal maternal blood triple marker screen (AChE, UE3, AFP)
  • Abnormalities found on ultrasound examination
  • Known metabolic disorder (inborn error of metabolism) for which prenatal diagnosis is available
  • Known molecular genetic disease for which prenatal diagnosis is available
  • Abnormal mosaic findings on CVS during the first trimester
  • Increased nuchal thickening observed by prenatal ultrasound


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