Oral contraceptive use is known to cause changes in the haemostatic system. These changes are thought to be related to oestrogen dose and to provide a possible link between the increased risk of thromboembolic disease known to occur in women taking oestrogen containing oral contraceptives. This study measured whole blood platelet activation, serially, in women taking oral contraceptives containing 20 micrograms and 30 micrograms ethinyloestradiol combined with desogestrel. Increased levels of ADP and arachidonic acid induced aggregation were observed in women taking the 30 micrograms ethinyloestradiol combination. Platelet release of beta-thromboglobulin (beta TG) was also significantly increased. Increased collagen induced aggregation was observed but this failed to reach statistical significance for the individual treatment groups. In women taking the 20 micrograms ethinyloestradiol combination, a significant increase was only observed when platelets were stimulated with arachidonic acid. Platelet factor 4 (PF4) levels were unchanged in both groups. Significantly higher levels of beta TG were observed in women taking the 30 micrograms ethinyloestradiol combination compared with women taking the 20 micrograms ethinyloestradiol combination. These results show that oral contraceptive use is associated with platelet activation. Women taking the 20 micrograms ethinyloestradiol combination show less changes in platelet activation than women taking the 30 micrograms ethinyloestradiol combination. This lower dose pill may therefore be particularly suitable for high risk women wishing to use oral contraception.
PIP: To evaluate the effects of low-dose oral contraceptives (OCs) on platelet function, hematologic measures were compared in 45 Irish women taking OCs containing 20 or 30 mcg of ethinyl estradiol as well as 150 mcg of desogestrel. Serum samples were collected before treatment and at 6, 14, and 22 weeks after OC use commenced. ADP induced whole blood platelet aggregation was significantly increased in users of OCs containing 30 mcg of ethinyl estradiol, reaching a maximum at 22 weeks, but not in users of the low-dose OC. A significant increase in collagen induced aggregation was observed when both groups of OC users were combined, but not when either was tabulated separately. Both groups showed significant increases in arachidonic acid induced aggregation. Platelet count, hematocrit, and platelet factor 4 levels were unaffected. Increased levels of beta-thromboglobulin were observed at 6, 14, and 22 weeks in the 30 mcg group; there was no significant change in the 20 mcg group. Since the low-dose 20 mcg ethinyl estradiol OC produced fewer changes in platelet activation, its use is recommended for women with risk factors for thromboembolic disease.