This is news to me. I will ask my mw next week too. With DS1 I kept taking the same prenatals the whole 40 weeks and continued for a year after because I nursed. No one told me to stop the folic acid.
One thing my mw did tell me is stop taking vitamins with DHA past 36 weeks. I forget why though. My prenatals do have DHA in them. Now I'll have to get some new vitamins just for that. :(