Chorionic Villus Sampling
What is the test?
Chorionic villi are small branching structures on one side of the placenta. They anchor the placenta to the wall of the uterus, almost like the roots of a plant. They have another root-like function, which is to absorb nutrients from the mother's blood in the lining of her uterus, and to deliver these to the umbilical cord. These structures contain cells from the developing fetus. A test that removes a sample of these cells through a needle is called chorionic villus sampling (CVS).
CVS answers many of the same questions as amniocentesis about diseases that the baby might have. Diseases that can be diagnosed with CVS include Tay-Sachs, sickle cell anemia, cystic fibrosis, thalassemia, and Down syndrome. (Rh incompatibility and neural tube defects, however, can be diagnosed only through amniocentesis.) CVS can be done earlier in pregnancy than amniocentesis and can be done when there is not enough amniotic fluid to allow amniocentesis. However, it has some extra risks when compared with amniocentesis.