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
Which of the following anticoagulant is safest in pregnancy? 
Select and explain. 
A. Warfarin, B. Heparin, C. Phenindione, D. Dicumarol
B: Heparin
Answer: B: Heparin 
Explanation: 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.