“…Twenty of them were performed in Europe [ 21 – 25 , 30 , 32 – 36 , 38 – 40 , 42 , 44 , 46 , 47 , 49 , 50 ]. Fifteen studies were of prospective nature [ 22 – 25 , 28 , 30 , 31 , 36 , 38 , 39 , 41 , 44 , 45 , 47 , 48 ]. Eleven studies were comparative cohort studies with a control group in which anticoagulation was not given [ 14 , 21 , 22 , 25 , 27 , 34 , 36 , 40 , 42 , 46 , 48 ].…”