Oral contraceptives, thrombosis and haemostasis

The use of oral contraceptives is a well-established acquired risk factor f or venous thrombosis. In 1995, a number of epidemiological studies were pub lished which suggested that women who use third generation oral contracepti ves that contain desogestrel or gestodene as progestagen are exposed to a t wo- to threefold higher risk for venous thrombosis than women using second generation oral contraceptives which contain levonorgestrel. In this paper, the effects of oral contraceptives on the haemostatic system are discussed . It appears that plasma from oral contraceptive users is resistant to the anticoagulant action of activated protein C (APC). This phenomenon, called acquired APC resistance, is more pronounced in users of desogestrel or gest odene-containing oral contraceptives than in women who use oral contracepti ve pills with levonorgestrel. On the basis of these observations, it was pr oposed that acquired APC resistance may be the mechanistic basis of the inc reased risk for venous thrombosis during oral contraceptive use and for the further increased thrombotic risk of third generation oral contraceptive u sers. Furthermore? the results of a recent cross-over study are discussed. This study indicated that a large number of other haemostatic parameters we re changed during oral contraceptive use. Some of these changes were more p ronounced on desogestrel-containing oral contraceptives. The cross-over stu dy also showed that the increased fibrinolytic activity during OC use is co unterbalanced by an enhanced activity of thombin-activatable fibrinolysis i nhibitor (TAFI), a protein that participates in the inhibition of fibrinoly sis. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.