It is usually done about 10-12 weeks from the woman's last menstrual period. This allows for earlier detection of birth defects. Like amniocentesis, CVS is performed in a hospital or the health care provider's office. CVS is a somewhat newer test than amniocentesis and is not available in all areas. The Procedure When CVS is performed, a small sample of cells is taken from the placenta where it is attached to the wall of the uterus.
Chorionic villi are tiny parts of the placenta.
Villi are formed from the fertilized egg, and have the same genes as the fetus. To collect cells through the vagina, a speculum is inserted just as for a Pap test. Then, a very thin, plastic tube is inserted into the vagina and up through the cervix . With ultrasound, the tube is guided to the placenta. A small sample is removed.