The condition in which a clot forms in the deep veins of the legs is called deep vein thrombosis(DVT). It can be divided into two types according to its location. It is called proximal or distal according to the veins it effects. If it effects veins of thighs its called proximal DVT. If it involves calf veins its called distal DVT. Risk factors for developing a DVT include: History of pulmonary embolism, cancers, smoking, family history of the condition, human IVIG products, extended immobilization such as post-surgery, medications like OCPs or SERMs, obesity, PICC lines or pregnancy.