Progesterone oral contraception and blood coagulation.

The effects on blood coagulation of oral contraception with continuous progestorone (0.5 mg chlormadinone acetate daily for 3 months) were studied in 76 women 37 (group 1) who had not previously taken any oral contraceptive and 23 (group 2) who had already been taking some combined or sequential preparations. Group 1 women had no significant increase in coagulability and platelet aggregation though an increase in fibrinolytic activity was suggested. Those tested by thromboelastography in this group showed no change in their thromboelastographic pattern. Before chlormadinone therapy group 2 women showed significant shortening of the prothrombin time and raised levels of factors VII and X. By the second month of chlormadinone administration the prothrombin time was normal. After the third month the factor VII level was no longer significantly increased but factor X although falling was still significantly high. Test results are encouraging for use of progesterone alone. Long-term work must be done to substantiate whether the thrombogenic element in the conventional oral contraceptive may have been eliminated by the use of progesterone alone.