Summary
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 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.
