Clinicians are occasionally faced with the dilemma of managing pregnant patients who require ongoing anticoagulation. Examples include women with mechanical heart valves, venous thromboembolism, and chronic atrial fibrillation. Methods : A prospective study randomly assigned 33 pregnant women aged between 22 and 43 years (average; 28.4); to receive either fractionated heparin: Enoxaparin (The 1st group, n = 17) or unfractionated heparin (The second group, n=16). In both groups, patients were given heparin (fractionated or unfractionated) during the 1st trimester and last month of pregnancy, and took warfarin between the 4th and 8th month.