Sixteen RCTs (6,055 patients) were included.
Mortality (12 RCTs, 5,364 patients): LMWH significantly reduced mortality in comparison with UFH; the OR was 0.68 (95% CI: 0.53, 0.88). No significant heterogeneity was found (P=0.75).
Recurrent VTE (13 RCTs, 5,568 patients): LMWH significantly reduced recurrent VTE in comparison with UFH; the OR was 0.66 (95% CI: 0.51, 0.86). No significant heterogeneity was found (P=0.1).
Major bleeding (16 RCTs, 6,055 patients): LMWH significantly reduced major bleeding in comparison with UFH; the OR was 0.56 (95% CI: 0.38, 0.83). No significant heterogeneity was found (P=0.3).
Different LMWHs: the scatter plot indicated that most LMWHs had greater efficacy and safety than standard UFH treatment. However, there was considerable variation between different LMWHs and also between studies using a single LMWH. The log OR of major bleeding ranged from 0.23 to -0.89 and the log OR of recurrent VTE ranged from 0.88 to -0.89.