According to this link, if you already had one baby with Spina Bifida, the chances are 4% that your next child will also have it.
Best wishes for a healthy baby -
http://www.marchofdimes.com/pnhec/4439_1224.asp
Good luck with everything, and FOLIC ACID/FOLATE is something you really need to take now and keep taking throughout this pregnancy it helps to prevent Spina Bifida. Make sure your doc runs the Triple Screen, he may even do an Amnio because it has happened to you before. Really, Good luck and please take lots of folic acid, folate is better (some women can't turn the folic acid into folate - which is what you need)