there is a very long thread on this board that you might want to read, b/c it discusses your exact question, but i'll let you know what i said to that post.
i was the first child, i have cf. my parents chose to have 2 more children, they are both without cf. but we would love them just as much if they had it!!!
it is a 25% chance. i think you just need to decide whether or not you would mind having another cf child, just in case. my parents were obviously ok with that chance, but luckily both of my sisters ended up being part of the 75%.
good luck with your decision. i would just say decide what YOU want, and if you decide you want more kids, don't let anyone talk you wout of it, and if you decide you don't, then don't let anyone talk you into it! <img src="i/expressions/face-icon-small-smile.gif" border="0">