This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematology, Subject name: Pharmacology
[{'content': 'Which of the following anticoagulant is safest in pregnancy? \nSelect and explain. \nA. Warfarin, B. Heparin, C. Phenindione, D. Dicumarol', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Oral anticoagulants like warfarin, phenindione and dicumarol can cross placenta and produce teratogenicity if used during pregnancy. Heparin does not cross placenta and is safe in pregnancy.', 'role': 'assistant'}]