I find it interesting how many different disciplines use the same acronyms. In the obstetrical field you will more often hear the acronym CVS than the full name of the procedure.
Chorionic Villus Sampling as a procedure is very well covered in this other node. The basics (so you will know if you do not want to look further) is that CVS is a form of obstetrical prenatal testing used to make a genetic diagnosis.
CVS allows the diagnosis of some genetic disorders very early in pregnancy. That is its advantage over amniocentesis as CVS and amnio basically diagnose the same genetic conditions.
Frequently when a woman is seeking genetic testing of her fetus it is with the intention to abort if the diagnosis is not the one desired. An abortion early in the pregnancy causes less maternal complications than an abortion later in the pregnancy.
Abortions performed after genetic testing can follow the diagnosis of conditions with extreme and unvarying mortality and morbidity, such as Tay Sachs disease to conditions with somewhat lessening mortality and morbidity such Cystic Fibrosis (as medical science improves outcomes). Genetic testing is also used to diagnose and often abort fetuses with even more controversical conditions, such as Down's syndrome. Prenatal genetic testing is even used for sex selection with fetuses of the undesired sex being aborted. Prenatal genetic testing is not always accurate. I have personally witnessed births of the "wrong" sex as well as "normal" infants who were diagnosed with genetic disorders during pregnancy.
CVS causes the loss of the pregnancy about 2% of the times it is used because of the invasive nature of the procedure.
Without even getting into the abortion debate, in my opinion it seems foolishly invasive to use the more dangerous procedure of CVS over amniocentesis if the intention is not a possible abortion but rather to know a diagnosis a little earlier. Sometime knowing a diagnosis prenatally can save the life of a child by allowing proper preparation for needed medical procedures immediately after birth but a few weeks to a month earlier do not matter for this particular rationale.