Thrombophilia is the propensity to evelop thrombosis (blood clots) due to an abnormality in the system of coagulation. Hereditary defects in one or more of the clotting factors can cause the formation of potentially dangerous blood clots (thrombosis). Approximately 5-8% of the U.S. population has one of these clotting disorders collectively called thrombophilia, a propensity for blood clotting in which a genetic defect can be identified that often results in thrombosis.