Chorion vili sampling
A prenatal diagnostic test that detects chromosomal abnormalities in a fetus. It involves the villi (hairlike projections) that compose the chorion (the outer layer of the amniotic sac). Cells from the villi provide chromosome information as do the cells from the amniotic fluid. A CVS test can be performed between the 9th and 12th weeks of pregnancy, providing earlier diagnosis than amniotic fluid studies.