Clotting Factors during Oral Contraception: Further Report

Coagulation studies were performed on 97 women taking a variety of oral contraceptives (OCs) 100 normal control women and 76 pregnant women (13 in the first trimester 26 in the second and 37 in the third). Prothrombin activity cephaline time and factor 7 8 and 10 assays were performed before the start and after 1 2 and 3 months then between 3-6 months 7-12 months and between 1-2 years. Prothrombin activity showed only slight variation throughout. There was little difference in cephalin time between the OC and the normal group. In contrast the pregnant patients showed progressively shorter cephalin times which became shortened during the second trimester the most marked acceleration occurring postpartum. There was little change in factor 7 during the first trimester of pregnancy but from the second trimester on a rise was recorded. A rise in factor 7 and 10 levels was seen from the third month on with the maximum in those patients who had been on OCs for more than 2 years. A broader spectrum of clotting tests appeared to be accelerated during normal pregnancy than during OC therapy and both factor 7 and 10 were higher when comparing trimesters of pregnancy with a similar period on OCs. After a 2 year course the rise in factor 7 levels was of the same order. It was concluded that it is important to determine whether factor 7 goes on increasing with more prolonged courses of oral contraception.