American Board of Internal Medicine (ABIM) Certification Practice Exam

During weeks 6-12 of pregnancy, what is the anticoagulation method recommended if the warfarin dose to maintain a therapeutic INR is less than or equal to 5 mg?

1. Weight-based LMWH

2. Unfractionated Heparin (UFH)

3. Direct oral anticoagulants

4. Factor Xa inhibitors

The correct answer is: Unfractionated Heparin (UFH)

The correct choice involves the recommendation of unfractionated heparin (UFH) as the preferred anticoagulation method during weeks 6-12 of pregnancy, specifically when the warfarin dose required to maintain a therapeutic International Normalized Ratio (INR) is low, at or below 5 mg. During pregnancy, especially in the first trimester, there's a critical need to avoid medications that may adversely affect fetal development. Warfarin is contraindicated during pregnancy due to its teratogenic effects, particularly during the first trimester, which means alternative anticoagulation strategies must be employed. Unfractionated heparin is favored because it does not cross the placenta and thus poses minimal risk to the developing fetus compared to other anticoagulation options. Unlike direct oral anticoagulants or low-molecular-weight heparin, UFH can be precisely dosed and monitored, allowing for adjustments based on the patient's needs, especially in the context of changing physiology throughout pregnancy. Additionally, it is conventional to manage the anticoagulation meticulously in this sensitive period (weeks 6-12), and the use of UFH aligns well with the clinical guidelines aimed at ensuring both maternal safety and fetal well-being during this crucial stage of development.