A prenatal diagnostic test, done at 8-10 weeks of pregnancy to asses the fetus' chromosomes. However, the risks to the fetus are greater than with amniocentesis.
Chorionic villi are a part of the placenta but contain fetal tissue.
A needle is inserted into the chorionic villi of the placenta and a small amount of tissue is removed and sent for analysis. The placenta can be approached either through the cervix or through the mother's abdominal wall. The results are available in about 5-10 days, sooner than with routine amniocentesis. There have been concerns about the procedure itself causing malformations of the legs and arms.