A woman has O- and a man has O+ blood type. Can they have more than 1 kid?

Me and my boyfriend/fiance have O type blood. But I am negative and he is positive. If we were to have children, which we do plan on doing, I know it is possible for us to have at least one child... but can we have more than one child? Because i know after my first child with him, I cand evelop antibodies that can prevent me from having any more children with him. Is there any way this can prevented now with modern medical science?