Actually, MyUC there are quite a few GIs who now think it's better to jump to Remicade if the mesalamine drugs don't work, especially if the patient is prednisone dependent or the symptoms are quite severe. This is because if Remicade is going to work, it will usually work right away, whereas it takes quite some time for Imuran to start working.
As for pregnancy on Remicade, there are some women on the Crohn's board who have had perfectly healthy babies while on Remicade (and Humira). I've heard that Remicade doesn't cross the placenta until the third trimester, so it's possible to time infusions so you only have one infusion during the third trimester. Or, if you're doing well, you can get an infusion at the very end of the second trimester, then wait the 12 weeks and have another infusion just after the baby is born. The biggest concern with Remicade is that even if the babies are born healthy, they really don't know yet if there are any long-term consequences.
Status: Remission since May 2009!
Symptoms began in November 2008, ~4 weeks after giving birth to my son
Diagnosed with pancolitis on 1/30/09
Meds: Apriso (4 0.375g pills ONCE!! daily), mesalamine enema twice weekly, Natural Factors Ultimate probiotic 12/12 Formula, multivitamin. Used prednisone (starting dose 40 mg) to get into remission.