Background: The management of women with prothetic valves During pregnancy remains challenging. Anticoagulation in these subgroups has many controversies. We aim to evaluate the safe dose of oral anticoagulant in pregnant women with mechanical valve prosthesis in first trimester. Methods: Pregnant ladies with well functioning prothetic valves were enrolled. Patients were divided into 3 groups: Group A took oral anticoagulant < 5 mg warfarin with therapeutic INR. Group B took low molecular weight heparin (LMWH) twice daily and monitoring is done every week by antifactor Xa 4-6 hours post-injection to keep about 1 IU/ml. Group C took oral anticoagulant in dose > 5 mg warfarin to reach therapeutic INR. Results: There was significant difference between groups in vaginal bleeding and abortion, with more bleeding and abortion in group B using LMWH. There was a high rate of malfunction valve about 19.9% in group B, but no reported cases of malfunction valve in the other both groups using warfarin. Conclusion: Warfarin with dose > 5 mg in pregnant women with mechanical prosthetic valve is as safe for mother and baby as warfarin with dose < 5 mg. Both regimens are safer than LMWH.