Expired prenatal vitamins?

The bottle I'm using now expires in October, but there's enough in it to last me through December. Is it okay to use them for a couple months after they expire? Or should I toss them and get new ones after October? I know vitamins lose there potency over time after they expire, but I wasn't sure how quickly that would be. I'm 10 weeks now, so I'll be 18-26 weeks Nov-Dec. Not sure if that makes any difference lol