MommaMary,
I just wanted you to know, although I don't have answers for you---that I'm in the same boat as you!!!!!! I am 11wks pregnant due in December---I am also on Dilantin--500mgs per day.........Didn't have insurance when I had my 1st seizure this past Jan.......So I have only seen my neurologist 1 time & when I told him I was pregnant--He just said I needed to start taking 4mgs/4000mmgs of Folic Acid........I will now be seeking a new neuro that will accept my insurance now that I'm getting assistance during my pregnancy...........
I have talked to other women that have been pregnant & nursed on Dilantin with no problems----so there is hope for us---I don't know about you, but I am a nursing mom & I was really hoping to be able to still do that....I have 4 children (ages 11,10,6 & 2) and I nursed all of them from 2 1/2 mos. to 18mos........
Anyways---I hope I have helped in any way-------Congratulations on your pregnancy!!!!
I'm sure everything will be fine!!!!!!!!! 
-----Jennifer