Other conditions including some cancers can also lead to a hypercoagulable state. Orthopedic surgery, especially on the hips or legs can increase the risk of thrombosis for several months. Chest, abdominal and bladder surgery can also do so, although less frequently. Pregnancy , and the use of estrogens either in birth control pills or as hormone replacement can lead to increased coagulability. A history of a previous deep vein thrombosis is also a risk factor.
Liquor tends to lead to dehydration, which in turn increases the coagulability of the blood.
Varicose veins, which are very common enlargements of the surface veins of the legs, are rarely the source of pulmonary emboli. One can form clots in varicose veins , a condition called thrombophlebitis, meaning inflammation of a vein with thrombosis, but these rarely give rise to pulmonary emboli. Since most of us never get tested to see if we have Protein C or S deficiency, don't often fly after serious orthopedic or other surgeries, and have never had a previous deep vein thrombosis we don't really know if we are at increased risk. To prevent stasis, don't wear constricting clothing, and move the legs regularly, preferably by getting up and walking in the aisles for a couple of minutes. Nobody wants to annoy the people sitting between them and the aisle by getting up frequently, but consider that you are actually doing them a favor by forcing them to stand and move into the aisle, thereby preventing stasis in their legs.