I wanted to know the answer to the same question, as I am only 26 and plan on having kids. I take both imuran and remicade.
**I was told by 2 different GIs that research has shown that women who took either of these drugs had the same amount of birth defects as the general population (meaning there is no increased harm to the fetus if you are on these drugs).**
I also met with a leading Crohn's research doctor (I had to wait 6 months to even get to see him), because my GI wanted me to also hear the answer to this question from someone doing active research on it. He told me the exact same thing--that women in his research showed no increase in birth defects while on either med.
Also, I have read many posts here of women having healthy babies while on the drugs. If your Crohn's is moderate/severe, it is a much better to be on meds while getting pregnant so as not to risk harm to the baby when/if you go into a flare!
Do some research on the Net and see for yourself. Google "imuran and pregnancy," or something like that, and read the most recent medical journal articles.
I hope all works out well for you!!!