Comparison 3. Heparin started before versus after the surgical procedure.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
3.1 Venous thromboembolism	1	100	Risk Ratio (M‐H, Fixed, 95% CI)	0.11 [0.01, 2.01]
3.2 Major bleeding	1	100	Risk Ratio (M‐H, Fixed, 95% CI)	3.00 [0.13, 71.92]
3.3 All‐cause mortality	1	100	Risk Ratio (M‐H, Fixed, 95% CI)	Not estimable
3.4 Venous thromboembolism‐related mortality	1	100	Risk Ratio (M‐H, Fixed, 95% CI)	Not estimable
3.5 Deep vein thrombosis	1	100	Risk Ratio (M‐H, Fixed, 95% CI)	0.11 [0.01, 2.01]