The risks of venous thromboembolism with hormonal contraception are well publicised, but the risks of arterial thrombotic complications are less well described with conflicting studies in the literature pertaining to the risk of myocardial infarction and stroke.  In this retrospective cohort study of the entire Danish population of women aged 15 to 49 years old, Lidegaard et al describe the outcomes for a total of 1,626,158 women accruing some 14,251,063 person-years of observation.  Using a number of national databases linked by unique personal identifying numbers, data was gathered on the use of hormonal contraception, clinical end points, and potential confounders including smoking.  During the 15-year study period, a total of 3311 thrombotic strokes (21.4 per 100,000 person-years) and 1725 myocardial infarctions (10.1 per 100,000 person-years) occurred in this essentially low risk population.  A wide variety of different drug formulations were available on the market and these were individually examined by progestin type and estradiol dose.  When estradiol was present at 30-40 μg relative risk of arterial events increased by a factor of 1.3 to 2.3 and this was broadly similar across all progestin types.   When estradiol was present at the lower dose of 20 μg relative risk of arterial events were increased only by a factor of 0.9 to 1.7, again being broadly similar across progestin types.

Conclusions

In this extremely large cohort study, hormonal contraception was seen to increase the risk of arterial thrombotic episodes with a dose-response relationship evident for estradiol levels. It should be emphasised however that the absolute risks of any arterial thrombotic complication were extremely low.

•  Lidegaard Ø, Løkkegaard E, Jensen A, Skovlund CW, Keiding N.  Thrombotic stroke and myocardial infarction with hormonal contraception.  N Engl J Med. 2012 Jun 14;366(24):2257-66.