I'm so sorry you're having to deal with this extra worry millerkat. It's hard enough deciding to put these drugs into our own bodies at times, let alone having to consider the risk that's being passed on to an unborn child. No one can tell you what to do, but remember that you flaring also carries risks to the baby so it's a case of choosing the lesser of two evils.
I second what my little penguin said about enteral nutrition. It doesn't work for everyone but at the least it might buy you some time until you're into your second trimester and can start steroids, at best it might save you from needing steroids at all. You could also consider Entocort rather than pred, which although it is still a steroid less of it is absorbed. Its use may be restricted depending on where abouts your inflammation is though - I think it targets the TI area. You could also try increasing your dose of Pentasa if you have room to. In the past that has been enough to bring flares under control for me.
I hope you can get the flare under control and can enjoy the rest of your pregnancy.