The effect of oestrogen dose and progestogen type on haemostatic changes in women taking low dose oral contraceptives.

OBJECTIVE

To determine the effect of oestrogen dose and progestogen type on the coagulation and fibrinolytic systems of a group of normal healthy women taking three different oral contraceptive combinations.

DESIGN

Plasma levels of factor VII, X, antithrombin III, protein C, fibrinogen, tissue plasminogen activator activity, plasminogen activator inhibitor I antigen and fibrin (D-dimer) degradation products were measured at pretreatment, 6, 14, 22 weeks of treatment and at 6 weeks post-treatment in a group of 67 women taking either 30 micrograms ethinyloestradiol/150 micrograms desogestrel (n = 21), 20 micrograms ethinyloestradiol/150 micrograms desogestrel (n = 24), 30 micrograms ethinyloestradiol/75 micrograms gestodene (n = 22).

PARTICIPANTS

Sixty-seven healthy normal women, 18 to 34 years, smoking fewer than 15 cigarettes per day. The subjects were within 10% of their normal body weight and had no history of thromboembolic disease.

SETTING

Coombe Women's Hospital and St James's Hospital, Dublin, Ireland.

RESULTS

Factor VII and X levels were significantly raised on treatment with both the 30 micrograms ethinyloestradiol/desogestrel and gestodene combinations. Higher levels of factor VII activity were observed in the 30 micrograms ethinyloestradiol/desogestrel combination compared with the gestodene combination. Factor VII and X were not significantly affected by the 20 micrograms ethinyloestradiol combination. Increased plasminogen, fibrinogen and D-dimer levels and decreased plasminogen activator inhibitor I antigen levels were observed during the treatment phases in all three groups. Antithrombin III and protein C activity did not change during treatment with any of the oral contraceptives studied.

CONCLUSIONS

Low dose oral contraceptives cause an activation of the coagulation system which is balanced by an activation of the fibrinolytic system. Reducing the dose of ethinyloestradiol from 30 micrograms to 20 micrograms reduces the effect on factor VII and X. This effect can be modified by the progestogen. The lesser effect of the 20 micrograms combination may make this a safer option for some women than pills containing a higher dose of oestrogen.