The vascular risks associated with combined oral contraceptives

Studying the vascular risks associated with a particular combined oral contraceptive is challenging, partly because venous and arterial events are uncommon in young predominantly healthy women and partly because there are large differences in the market share of different formulations. Traditional epidemiological studies established specifically to investigate the issue tend to be costly and prolonged and often lack statistical power when comparing different products. To overcome these problems, several research groups have used the growing opportunity provided by computerised clinical data collected during everyday practice.

In this issue, Weill and colleagues (doi:10.1136/bmj.i2002) used data about eight combined oral contraceptives reimbursed by the national health insurance system in France between 2010 and 2012 linked to national hospital discharge data.1 The linked dataset contained 5.4 million woman years of oral contraceptive use, during which 1800 pulmonary emboli, 1046 ischaemic strokes, and 407 myocardial infarctions occurred. This enabled precise point estimates to be obtained for each …