Influence of modern low-dose oral contraceptives on hemostasis.

Several reports have appeared on the increased risk of thromboembolic diseases associated with the use of oral contraceptives (OCs). The increased risk of thromboembolism has been related to increased circulating blood levels of certain factors of both the clotting and fibrinolytic systems seen in OC users. These changes have been associated primarily with the estrogen component of the OC preparations. The two new oral contraceptives under study contain reduced levels of ethinyl estradiol, 30 micrograms and each utilizes a new progestogen--75 micrograms gestodene or 150 micrograms desogestrel. A prospective randomized study was performed with 50 women over one year in which several factors of the hemostatic system were investigated; blood samples were taken in treatment cycles 1, 3, 6 and 12 and 6-8 weeks after cessation of therapy. During treatment with both preparations, factors II, VII, IX, X, XI, XII, VIII clotting activity, and prekallikrein were elevated; factor V was not elevated. Antithrombin III which controls these factors, was decreased by 8-10% after 12 months; Protein C which controls factors V and VIII was not changed. Markedly elevated levels of plasminogen and its unaffected inhibitor alpha antiplasmin were seen in the first and all subsequent treatment cycles; this represents increased potency of the lytic system, which can be looked upon as a compensatory mechanism. There were no differences seen between the gestodene and desogestrel preparations regarding changes in the hemostatic system. As with all other low-dose pills, a history of thromboembolism is a contraindication to their use.