Seven RCTs (8,902 participants) were included: six on LMWH (8,053 participants) and one on fondaparinux (849 participants). No studies on unfractionated heparin were included.
Results for fixed-effect and random-effects models were similar; those for fixed-effect were reported. The p value for heterogeneity was above 0.10 in all analyses.
Treatment with LMWH or fondaparinux reduced the risk of asymptomatic DVT (RR 0.49, 95% CI 0.38 to 0.64, NNT 33; five studies) and of symptomatic pulmonary embolism (RR 0.52, 95% CI 0.29 to 0.91, NNT 241; seven studies). The risk of symptomatic DVT was also reduced, but did not reach statistical significance (RR 0.52, 95% CI 0.25 to 1.08, NNT 271; five studies). There was a trend towards a higher risk of major bleeding, but this was not statistically significant (RR 1.39, 95% CI 0.77 to 2.51, NNH 598; seven studies). There was no difference in all-cause mortality (RR 0.95, 95% CI 0.79 to 1.14; seven studies).