Final answer:
The physician changed the anticoagulant from warfarin (Coumadin) to enoxaparin (Lovenox) to reduce the risk of bleeding in the pregnant patient.
Step-by-step explanation:
The best rationale for the physician changing the anticoagulant from warfarin (Coumadin) to enoxaparin (Lovenox) is that the patient is less likely to have bleeding with enoxaparin (Lovenox). Warfarin, on the other hand, can increase the risk of bleeding. Enoxaparin (Lovenox) is a low molecular weight heparin and is frequently given to pregnant women instead of warfarin due to its reduced bleeding risk.