The chorion is the portion of fetal membrane that eventually forms the fetal side of the placenta. The chorion contains chorionic villi which are small finger-like projections. These villi are snipped or suctioned off for study in the procedure. The chorionic villi are of fetal origin so examining the samples of them can give the genetic makeup of the fetus. This test is performed as an early detection tool of congenital defects. The sample is used to study the DNA, chromosomes, and enzymes of the fetus; and can be done before amniocentesis, about 10 to 12 weeks after a missed period.

Review Date: 12/5/2001 12:00:00 AM Reviewed By:A.D.A.M. Medical Illustration Team

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