We haven't said anything about CVS's, because most places we consult with have stopped doing them. However, a lot of the mail to AmnioNet concerns CVS, so we thought we should devote a little time to this technique for early pregnancy genetic testing. The chorionic villi are within the trophoblastic layer that surrounds the gestational sac early in development. This tissue will give rise to the placenta.
Chorionic villi are fetal derived cells with a full set of fetal chromosomes.
CVS is a biopsy procedure, removing a tissue sample that contains dividing cells whose chromosome patterns can be evaluated directly without the need to culture individual cells for 5 to 7 days first. But there are some serious problems. When CVS was introduced, sampling was with a firm catheter that has to be passed through a closed cervix. Catheter passage and aspiration of villi may hurt, can disrupt attachment of the sac, and can be complicated by bleeding and infection. When villi are disrupted and sucked up through a needle, lots of material is released into the embryonic circulation forming emboli that can disrupt blood flow in other parts of the body.