Fibrinopeptide A plasma levels during low-estrogen oral contraceptive treatment.

In a group of healthy women taking oral contraceptives containing 30 micrograms ethinylestradiol combined with two different progestogens (desogestrel and gestoden), Fibrinopeptide A (FPA) plasma levels were evaluated both before and after 3, 6 and 9 months of therapy. FPA levels, which represent an index of thrombin action in vivo, were also determined in untreated subjects during the follicular and the luteal phases of the menstrual cycle. While no modifications of FPA levels were found during the menstrual cycle, a significant increase of this peptide was observed during oral contraceptive treatment. These data suggest that low-dose oral contraceptives, by enhancing the rate of conversion of fibrinogen to fibrin by thrombin, increase the risk of venous thrombosis. Since some mechanisms which compete with the thrombin activity are also increased by oral contraceptives, the significance of this change in the induction of thrombosis cannot be completely clarified.