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Villi, or villous cells of the anchor chorion, are active migrating cells that take part in the formation of the placenta in the first trimester of pregnancy. Already from 7 weeks of pregnancy, after the formation of the morula and blastocyst, the chorionic villi begin to secrete epithelial trophoblast. It is from this moment that the active development of villi occurs. The cells of the anchor zone, having separated from the wall of the uterus and secured to the membrane of the villi with chorionic tissue, are able to fully perform their specific functions aimed at ensuring a normal pregnancy and the birth of a full-fledged healthy child. The location of the chorionic villi determines whether the pregnancy will continue its normal course. If the villi are located along the walls of the uterus, then, as a rule, conception is successful. If the villi are evenly distributed over the entire area of the uterus, the pregnancy may be terminated.