An epidemiological study of the haemostatic and other effects of oral contraceptives

Abstract

Factors V, VII and VIII (each determined by biological assay), fibrinogen, platelet count and adhesiveness, and fibrinolytic activity were measured in 234 white pre-menopausal women, of whom 57 (24%) were on oral contraceptives and 177 (76%) were not. Cholesterol, triglyceride and blood pressure levels were also recorded. In 20 of the women on oral contraceptives, and in an age-matched group of 20 who were not, prothrombin, factor X, antithrombin III and alpha 2-macroglobulin levels were determined, and factors VII and VIII were also measured immunologically. For the majority of the variables studied, the differences between those using and not using oral contraceptives were greater in younger than older women; in the case of factor VII (biological assay) and fibrinogen, the differences between the regression slopes on age were statistically significant, and mean values were substantially higher in those on oral contraceptives. There was also a significant difference between regression slopes on age for cholesterol. Mean levels of prothrombin, factors VII (immunological assay) and X, triglycerides and blood pressure were significantly higher, and mean levels of antithrombin III significantly lower, in those on oral contraceptives compared with those not. Overall, fibrinolytic activity was significantly higher in the women on oral contraceptives; this difference was, however, almost entirely due to the greatly increased fibrinolytic activity of the non-smokers on oral contraceptives, activity in the smokers on oral contraceptives being similar to that of the women not on these preparations. There were no significant differences in mean platelet count or adhesiveness, or in haemoglobin, packed cell volume, uric acid and blood sugar levels. Among the women on oral contraceptives, there was a significant negative correlation between factor VIII and fibrinolytic activity; this was largely due to five women all of blood groups A and B, in whom, besides high factor-VIII levels and poor fibrinolytic activity, other variables (e.g. fibrinogen) were raised in a direction that might be expected to favour thrombogenesis. It is possible that it is those women whose fibrinolytic activity does not increase in order to compensate for the effects of oral contraceptives on clotting factors, lipids and blood pressure, who are at special risk of thromboembolic episodes. The differential effects of oral contraceptives by age must be borne in mind in evaluating the effects of these preparations on the haemostatic and lipid systems.

PIP: An epidemiological study of the hemostatic and other effects of oral contraceptives (OCs) is reported. Factors 5, 7, and 8, fibrinogen, platelet count, and adhesiveness, and fibrinolytic activity were measured in 234 white premenopausal women, of whom 24% were on OCs and 76% wer not. Blood pressure, cholesterol, and triglyceride levels were also recorded. In 20 of the women on OCs and in an age-matched group of 20 who were not, prothrombin, Factor 10, antithrombin 3, and alpha2-macroglobulin levels were determined and Factors 7 and 8 were also measured immunologically. Generally, the results revealed that the differnces between those using and not using OCs were greater in younger than older women. In the case of Factor 7 (biological assay) and fibrinogen, the differences between the regression slopes on age were statistically significant (p less than .05), and mean values were substantially higher in those on OCs. There was also a significant difference (p less than .005) between regression slopes on age for cholesterol. Mean levels of prothrombin, Factors 7 (immunological assay) and 10, triglycerides (p less than .001), and blood pressure (p less than .005 and less than .05) were significantly higher and mean levels of antithrombin 3 were significantly lower (p less than . 001) in those on OCs compared with those not on OCs. Overall, fibrinolytic activity was markedly higher in women on OCs which was almost entirely due to the greatly increased fibrinolytic activity of the nonsmokers on OCs; activity in the smokers on OCs was similar to that of those not on OCs. No marked differences in mean platelet count or adhesiveness, hemoglobin, packed cell volume, uric acid, and blood sugar levels were noted. There was significant negative correlation (r = -.4, p less than .01) between Factor 8 and fibrinolytic activity in women on OCs.