Venous thromboembolism and oral contraceptives

Risk of venous thromboembolism from oral contraceptives containing gestodene and desogestrel versus levonorgestrel: a meta-analysis and formal sensitivity analysis

Controversy exists regarding whether oral contraceptives (OCs) containing desogestrel and gestodene are associated with an increased risk of venous thromboembolism (VTE) versus OCs containing levonorgestrel. We were interested in synthesizing the available data, exploring explanations for mixed results, and characterizing the degree of uncontrolled confounding that could have produced a spurious association. We performed a meta-analysis and formal sensitivity analysis of studies that examined the relative risk of VTE for desogestrel and gestodene versus levonorgestrel. Twelve studies, all observational, were included. The summary relative risk (95% CI) was 1.7 (1.3-2.1; heterogeneity p = 0.09). If real, the incremental risk of VTE would be about 11 per 100,000 women per year. An association was present when accounting for duration of use and when restricted to the first year of use in new users. However, in the sensitivity analysis, the association abated in many, but not all, scenarios in which an unmeasured confounding factor increased the risk of VTE three to fivefold and in nearly all examined scenarios in which the factor increased the risk 10-fold. The summary relative risk of 1.7 does not appear to be caused by depletion of susceptibles, but is sensitive to a modest degree of unmeasured confounding. Whether such confounding occurred is unknown. However, given this sensitivity, this issue probably cannot be settled unequivocally with observational data. In the absence of a definitive answer, this apparent increased risk, together with its uncertainty and small magnitude and its important consequences, should be considered when selecting an OC for a given woman.

Cardiovascular events associated with different combined oral contraceptives: a review of current data

Studies of combined oral contraceptive (COC) use and cardiovascular disease have been conducted against a background of low cardiovascular risk in young women, changing COC composition and changing user selection and monitoring. Studies of myocardial infarction have found inconsistent results, possibly because of differences in the prevalence of risk factors (particularly smoking and raised blood pressure) in the populations studied. In the absence of a history of smoking and other conventional risk factors, current users of modern COCs probably do not have an increased risk of myocardial infarction. Neither are former users at risk. Evidence for important differences in the risk of myocardial infarction between formulations is weak and contradictory. Current users of low estrogen dose COCs have a small increased risk of ischaemic stroke although most of the risk occurs in women with other risk factors (notably smoking, hypertension and probably a history of migraine). Former users of COCs do not have an increased risk of ischaemic stroke. There is insufficient information to determine whether major differences in the risk of ischaemic stroke exist between products. Current users appear to have a modestly elevated risk of haemorrhagic stroke, mainly in women older than 35 years; former users do not. Data examining the risk of haemorrhagic stroke in current COC users with other risk factors are very sparse, as are those relating to the haemorrhagic stroke risk associated with particular COCs. Numerous studies have found, with remarkable consistency, an elevated risk of venous thromboembolism among current users of low estrogen dose COCs. The risk is substantially elevated among women with various inherited clotting factor defects. The effects in COC users with other risk factors for venous thrombosis tend to be less pronounced and more inconsistent. A number of studies have found higher relative risks among current users of low estrogen dose COCs containing desogestrel or gestodene, than among users of similar products containing levonorgestrel. A number of explanations, in terms of bias or confounding, have been proposed for these clinically small differences. At best, empirical evidence for these explanations, is weak. The risk of cardiovascular disease of any description is low in COC users. Women can minimise, and possibly eliminate entirely, their arterial risks by not smoking and by having their blood pressure checked before using a COC (in order to avoid its use if raised blood pressure is discovered). Users may decrease their venous thromboembolic risk by their choice of COC preparation although the effects will be modest.