This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Medical Illness Complicating Pregnancy, Subject name: Gynaecology & Obstetrics
Which vitamin deficiency is most commonly seen in a pregnant mother who is on phenytoin therapy for epilepsy? 
Select and explain. 
A. Vitamin B6, B. Vitamin B12, C. Vitamin A, D. Folic acid
D: Folic acid
Answer: D: Folic acid 
Explanation: Phenytoin inhibits the enzyme intestinal conjugase, an impoant enzyme in folic A. Metabolism. Folate is present in food in a polyglutamate form. This is conveed into monoglutamates by intestinal conjugase to be absorbed in the jejunum. Phenytoin acts by inhibiting this enzyme thereby causing folate deficiency and thus megaloblastic anemia.