Oral contraceptives and oestrogen replacement therapy as determinants of plasma fibrinogen level and fibrinolytic activity the northern sweden MONICA study

Abstract

Summary Objective : To investigate the relationship between the use of oral contraceptive pills (OC) or oestrogen replacement therapy (ORT), and haemostasis and fibrinolysis. Design : Cross-sectional population study. Setting : Population screening in the Northern Sweden MONICA Study. Material : 775 women between 25 and 64 years. Outcome measure : Plasma fibrinogen, tissue plasminogen activator (tPA) activity, tPA antigen and plasminogen activator inhibitor 1 (PAI-1) activity according to OC use in premenopausal and ORT use in postmenopausal women. Results : After adjusting for age, tPA antigen and PAI-1 activity were significantly lower in OC users compared to non-users. The differences remained statistically significant after adjusting for anthropometric and metabolic factors; tPA antigen levels were 26% lower and PAI-1 activity was 39% lower in OC users. No difference between the groups was found in fibrinogen and tPA activity. ORT users had significantly lower age-adjusted plasma fibrinogen and tPA antigen compared to the non-users. After adjusting for smoking, anthropometric and metabolic factors, the values were still lower, but the differences were no longer statistically significant. tPA activity and PAI-1 activity did not differ between the groups. Conclusion : Users of OC showed a favourable pattern in haemostatic or fibrinolytic variables when compared to non-users. Users of ORT did not differ from non-users in these variables after adjusting for possible confounders.