A vein thrombus occurs in the deep veins located in the legs of pelvis. The vein thrombus entails a clot that blocks the blood vessels causing serious health complications. Numerous risk factors may lead to development of a deep vein thrombus (DVT). These risk factors include a previous history of venous thromboembolism may cause a deep vein thrombus condition. Further, a previous episode of deep vein thrombus may also increase the chances of one developing a serious deep vein thrombosis condition.