[Venous thromboembolism and oral contraception]

Because of their safety and efficacy oral contraceptives are available without prescription in many countries. Monophasic combined oral contraceptives are a combination of estrogen and progestin taken in constant amounts.

Combined oral contraceptives slightly increase the risk of venous thromboemolism, but this event is very rare among non-pregnant women of reproductive age. The absolute risk rises with age, obesity, recent surgery and certain forms of thrombophilia. The estrogen component of combined oral contraceptives increases the synthesis of several coagulation factors in a dose-dependent manner. Changes of most of these parameters are very small and there is no evidence that they have any effect upon the clinical risk of developing venous thrombosis. If a woman has an inherited coagulation disorder that increases her risk of developing thrombosis, the risk is increased several fold if she ingests estrogen containing oral contraception.

The increased risk of venous thromboembolism associated with combined oral contraceptives should have little impact on healthy women, but may have substantial impact on women with a history of thromboembolism. Combined oral contraceptive use increases the risk of venous thromboembolosm in a dose-dependent manner. The absolute risk of venous thromboembolism rises with age, obesity, recent surgery and certain forms of thrombophilia, as well.