Objective To 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. Design Systematic review and meta-analysis. Data sources Medline. Studies reviewed Eight observational studies and nine randomised controlled trials. Inclusion criteria Studies on hormone replacement therapy that reported venous thromboembolism. Review measures Homogeneity between studies was analysed using χ 2 and I 2 statistics. Overall risk of venous thromboembolism was assessed from a fixed effects or random effects model. Results 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

We thank Drs Micheletti and Chevallier for their interest in our report. 1 First, we believe that odds ratios (ORs) and 95% confidence intervals (CIs) estimated from logistic regressions provide adequate information about significance and the size and direction of the effect of norpregnane derivatives. Because elevation in venous thromboembolism (VTE) risk is substantial (OR: 4) and significantly different from 1 (with the 95% CI not crossing 1), our results suggest a thrombogenic effect of norpregnanes, and the probability value (PϽ0.006) indicates that the probability of the result being due to chance is very small. Second, only the main effects of the route of estrogen administration and type of progestogens were estimated with a joint model ( Table 2 of the original article 1 ). Stratified analyses by route of estrogen administration and type of progestogens have also been performed. Among transdermal estrogen users, women received estrogen alone (10 cases and 35 controls; OR: 0.8, 95% CI: 0.4 to 1.8 after adjustment for obesity, family history of VTE, and varicose veins) or combined with either micronized progesterone (13 cases and 63 controls; OR: 0.6, 95% CI: 0.3 to 1.2), pregnane derivatives (16 cases and 51 controls; OR: 0.8, 95% CI: 0.4 to 1.6), or norpregnane derivatives (28 cases and 31 controls; OR: 3.1, 95% CI: 1.7 to 5.9). Among oral estrogen users, women received estrogen alone (4 cases and 5 controls) or combined with either micronized progesterone (6 cases and no controls), pregnane derivatives (23 cases and 28 controls), norpregnane derivatives (12 cases and 6 controls), or nortestosterone derivatives (12 cases and 7 controls). There was no significant difference in VTE risk between any of the progestogen subgroups among current users of oral estrogen (overall OR: 4.5, 95% CI: 2.6 to 7.5).Third, to allow for adequate numbers of subjects within subgroups, stratified analysis by time of exposure used the median of the distribution (5 years) as a cutoff point. Unlike oral estrogens, there was no significant interaction between the time of exposure to either transdermal estrogens or norpregnane derivatives and VTE risk. Therefore, differences in exposure time to hormone therapy cannot explain our results.Finally, although our results may be clinically relevant, we acknowledge that interpretation of data may have been biased by the inclusion of women with hyperestrogenic symptoms who were prescribed norpregnane derivatives. This prescription bias was emphasized in the Discussion section. Regarding the absence of thrombogenic mechanism underlying our results, Micheletti and Chevallier quote an inconclusive small trial 2 that failed to also show the well-known activation of blood coagulation among women using oral estrogens. In addition, relevant hemostatic tests such as plasmaactivated protein C sensitivity were not included as end points in this trial. Because relevant data are lacking, we are presently investigating the impact of norpregnanes on hemostasis among users of hormone therapy in the Stu...

The risk of deep vein thrombosis and pulmonary embolism after surgery is substantially increased in the first 12 postoperative weeks, and varies considerably by type of surgery. An estimated 1 in 140 middle aged women undergoing inpatient surgery in the UK will be admitted with venous thromboembolism during the 12 weeks after surgery (1 in 45 after hip or knee replacement and 1 in 85 after surgery for cancer), compared with 1 in 815 after day case surgery and only 1 in 6200 women during a 12 week period without surgery.