Congratulations on your pregnancy! I have never had children, but hope to soon so I have been doing a fair amount of my own 'research' on this topic. I took 6mp for about two years then stopped last winter with the hope of conceiving this year. 6mp is a class D pregnancy drug, however, the if the mother needs it to keep her and the baby safe it has still been used in pregnancy. My GI gave me a bunch of information on it to read and was very honest with me about his opinion. He looked me in the face and said "if you were my wife and carrying my child I would not want you on this drug" - we have a very straight forward relationship though! After that, he went on a bit more saying yes there are many risks with it during pregnancy, but the general concensus is that it 'can' be safe, particularly at lower doses. I've actually got an appt coming up in the next few weeks with a high risk OB/GYN about this very subject. I'm hoping that none of my doctors decide that I need to be on it during pregnancy.
In relation to your other question, everyone is so differenct with UC, but myself, I have had it for 11 years and I've been lucky enough to go for periods of a few years in remission. Right now I am on prednisone for the first time in 7 years, which I felt was a pretty good track record. Like I said though, everyone is very very different.
I hope you feel better and congratulations on the pregnancy again!!