Hormone replacement therapy and risk of venous thromboembolism in postmenopausal women: systematic review and meta-analysis.

International audienceTo assess the risk of venous thromboembolism in women using hormone replacement therapy by study design, characteristics of the therapy and venous thromboembolism, and clinical background. Systematic review and meta-analysis. Medline. Eight observational studies and nine randomised controlled trials. Studies on hormone replacement therapy that reported venous thromboembolism. REVIEW MEASURES: Homogeneity between studies was analysed using chi(2) and I(2) statistics. Overall risk of venous thromboembolism was assessed from a fixed effects or random effects model. Meta-analysis of observational studies showed that oral oestrogen but not transdermal oestrogen increased the risk of venous thromboembolism. Compared with non-users of oestrogen, the odds ratio of first time venous thromboembolism in current users of oral oestrogen was 2.5 (95% confidence interval 1.9 to 3.4) and in current users of transdermal oestrogen was 1.2 (0.9 to 1.7). Past users of oral oestrogen had a similar risk of venous thromboembolism to never users. The risk of venous thromboembolism in women using oral oestrogen was higher in the first year of treatment (4.0, 2.9 to 5.7) compared with treatment for more than one year (2.1, 1.3 to 3.8; P