One recent study of DVT in non-hospitalized patients found several potential risk factors, including increasing age (higher in the elderly), recent surgery, more than 3 pregnancies, previous DVT, and estrogen use (either as hormone replacement therapy or as oral contraceptives). Immobility has also be hypothesized as a leading factor for the development of clots.

See: Meyer-Michel Samama, MD (BiolPharm); for the Sirius Study Group

Arch Intern Med. 2000;160:3415-3420