SummaryOral 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 μg and 30 μg ethinyloestradiol combined with desogestrel. Increased levels of ADP and arachidonic acid induced aggregation were observed in women taking the 30 μg ethinyloestradiol combination. Platelet release of β-thromboglobulin (βTG) 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 μg 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 βTG were observed in women taking the 30 μg ethinyloestradiol combination compared with women taking the 20 μg ethinyloestradiol combination. These results show that oral contraceptive use is associated with platelet activation. Women taking the 20 μg ethinyloestradiol combination show less changes in platelet activation than women taking the 30 μg ethinyloestradiol combination. This lower dose pill may therefore be particularly suitable for high risk women wishing to use oral contraception.

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