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 drugs does not cross placenta? \nSelect and explain. \nA. Heparin, B. Warfarin, C. Dicumarol, D. Nicoumalone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Heparin due to its large molecular size does not cross the placental barrier therefore can be used in pregnancy. From medical pharmacology padmaja 4th edition Page no 335', 'role': 'assistant'}]