Why prescription prenatal vitamins?

ladychicago

So, with my first pregnancy, my OB never really talked about vitamins.   The nurse would sometimes ask me if I "had enough," but since I was buying OTC, I always said yes and left it at that.   

At my first OB appointment with this pregnancy last week, the nurse asked me about prenatal vitamins again.    I said I just took OTC ones, so I had plenty.    She gave me the side-eye and said my OB would definitely talk to me about that.     Well, when the OB came in, we dived into talking about the SCH and extra monitoring, and I forgot to ask.   and he didn't say anything.   But when I checked out, the lady making my appointments gave me a prescription for vitamins.   

I know I could call and ask the nurse...   but have any of you had this conversation with your OB?    Why prescription ones?  What is insufficient in the OTC?    Clearly, my daughter is amazing and awesome in every way (tee hee), so I don't really see the need...   but at the same time, my OB is pretty low key about most things, so if he recommends something enough to write a prescription, it makes me think he feels strongly about it.    I just want to know what the reasoning is, you know?