I used hydrocortisone enemas with my first pregnancy, which I am guessing would be similiar to the suppositories.
I was in a HORRIBLE flare when I was 6 weeks pregnant and they helped to get it back under control. I had to use them for 2-3 weeks and then was able to switch back to rowasa enemas and then tapered those down to once a week. You will have to see how the pregnancy goes. Some women flare and some stay in remission. I flared badly with my first pregnancy(but I was on NO meds like an idiot) and only had a very minor flare with my second. With both pregnancies I had pretty bad flares after giving birth. With my first it was 6 weeks after and my second it was 4 weeks after. Be prepared in case you do flare as you will need help with the newborn and trying to get yourself back in remission. That part is not fun if it happens to you. The hormones play a huge role in my UC symptoms. If you need anymore advice let me know.