Six RCTs were included (n= 1,456). Three studies were classified as high quality. All studies showed baseline similarity of treatment groups. Three studies used adequate allocation concealment, three were open-label, three were double-blinded and two reported adequate clinical follow-up. Three studies had a substantial drop-out rate (rates were not reported).
LMWH was associated with a statistically significant reduction in the risk of VTE compared to placebo or no treatment: 9.6 per cent versus 17.1 per cent; RR using random-effects model 0.58 (95% CI: 0.39, 0.86, p=0.006). Moderate heterogeneity was found (I2 45.4%).
Subgroup analyses: similar reductions in RR were found for the risk of proximal DVT, risk of VTE in patients with fractures or tendon ruptures and in the risk of VTE in high-quality studies (CIs for some analyses were wide). The NNT to prevent one asymptomatic DVT in prophylaxis compared to control groups was 13 (95% CI: 9, 25).
Bleeding: there was no statistically significant difference between LMWH and control in the frequency of major or minor bleeding; RR 1.22 (95% CI: 0.61, 2.46, p=0.57 based on three studies involving 700 patients who had received LMWH).