GSTM1 and deep vein thrombosis: No significant differences were identified with regard to the Hb drop (SMD = − 0.03,95%CI = − 0.18–0.12, P = 0.67), total Hb loss (SMD = 0.10,95%CI = − 0.06–0.26, P = 0.24), total blood loss (SMD = − 0.00,95%CI = − 0.20–0.20, P = 1.00), transfusion rate (OR = 0.77,95%CI = 0.54–1.10, P = 0.14), DVT rate (OR = 0.58,95%CI = 0.19–1.75, P = 0.33), and length of hospital stay (SMD = − 0.05,95%CI = − 0.28–0.17, P = 0.63) between the oral groups and intravenous group.