Low-dose oral contraceptive usage and coagulation.

A prospective investigation was initiated to assess the effect of a low-dose oral contraceptive containing 35 micrograms of ethinyl estradiol and 0.4 mg of norethindrone on blood coagulation and fibrinolysis. Twenty-four women were studied before, during, and after one year of treatment. Positive results included an accelerated activated partial thromboplastin time and an increase in fibrinolytic and anticoagulation factors as measured by alpha 1-antitrypsin antigen and plasminogen antigen and activity. Antithrombin III antigen was decreased but its activity was unaffected. There was no evidence of ongoing intravascular coagulation. No patient had a detectable thromboembolic event. In short, one year's usage of this low-dose oral contraceptive was not associated with a procoagulant hematologic profile.