The Internet is a fountain of information, both true and false. One of the false claims concerning hCG is that it causes blood clots. Blood clots in the leg are occasionally diagnosed during pregnancy. This condition, called thrombophlebitis, is more likely to occur during pregnancy because of changes in blood circulation. Blood flow in the legs slows down (a condition called stasis) because of pressure from the uterus on blood vessels and because of changes in the blood and its clotting mechanisms.