First, congratulations!!!
I had severe UC and successfully carried 3 pregnancies to term. I absolutely had to be on Imuran the whole time; the benefits of taking the drug outweighed the risks. Also, I had read up on the research of a Mt. Sinai doctor who found that there is no risk of defects in infants born of mothers on Imuran. My three babies are a testament to that as well. They are now 8 1/2, 7, and 2 1/2 and very smart, healthy, and thriving.
I had an M/C at 8 weeks due to a horrible flare with my first pg, which is why I took the Imuran for all of the others. With my son and eldest daughter I was on a therapeutic dose and never flared the whole time. Right before my last pg I was not on Imuran although I was in remission without disease showing up at even a microscopic level. Within two weeks of a + pg test the UC was back. Within a month I went back on Imuran, and was back in remission a couple of weeks later. I proceeded through that pg, delivery, and post event free for about 8 months before Imuran stopped working for good.
The only negative about taking the drug in pg is that you cannot breastfeed. I was disappointed for sure, but I felt I was much healthier taking the drug than not, and a lot less stressed out about a flare. For me, I would get much more stressed out when flaring. It was always a vicious cycle.
They say the rule of thirds apply to pg and UC. One third stays the same, 1/3 improves, and 1/3 gets worse. Unfortunately, I was in the 1/3 that got worse.