This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
All of the following drugs are harmful in pregnancy except 
Select and explain. 
A. Phenytoin, B. Diazepam, C. Warfarin, D. Heparin
D: Heparin
Answer: D: Heparin 
Explanation: Heparin does not cross the placenta. Hence it is safe for use in pregnant patients who needs anticoagulation.Ref: Katzung 13th ed Pg 589