How effective are compression stockings at preventing dvt? is there a chance that blood would just pool in the thighs instead of in the calves?

Thigh high: Actually Amanda there are thigh hi compression stockings to prevent that. but for DVT talk to your doctor about anticoagulants. DVTs can cause bad things. Also BCP pills can make them worse. good luck

Fairly good: Thigh-high stockings are best but not every person will wear them. Calf (knee) height are good at preventing the venous reflux and stasis that leads to clotting. They can also prevent the veins from becoming varicose in later life so if you stand all day at your job, stockings are are good for keeping your legs looking good.

Studies are lacking: on the effect of compression stockings on DVT risk, particularly in healthy patients with or without varicose veins. We tend to recommend them based on our understanding of venous stasis, but there are no solid statistics. Calf stockings won't cause pooling higher up unless thigh veins have already failed. Even then, in theory, higher is better because there's less hydrostatic pressure higher.