Effect of oestrogen dose on whole blood platelet activation in women taking new low dose oral contraceptives.

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.