The condition in which a clot forms in the deep veins of the legs is called deep vein thrombosis(DVT). If it effects veins of thighs its called proximal DVT. If it involves calf muscles 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. VIrchow's triangle are the factors that increase the probability of development of a thrombosis. These are: venous stasis, vein damage or activation of blood coagulation factors. Symptoms of the condition include: pain, swelling or tenderness, dilated superficial vessels. Mostly DVT produces no symptoms and is seen with complications like pulmonary embolism.