Predictors of thromboprophylaxis failure as measured by development of venous thromboembolism included a personal or family history of venous thromboembolism ( hazard ratio , 1.64 ; 95 % CI , 1.03-2 .59 ; p = 0.04 ) and body mass index ( hazard ratio , 1.18 per 10-point increase ; 95 % CI , 1.04-1 .35 ; p = 0.01 ) .