Congratulations!!!
While I'm no expert, I WAS 6 months pregnant when I visited USF awhile ago. The rule of thumb that I was told before I went on my trip was that if a ride spins or drops, and therefore is pulling the blood away from your baby, then those things should be avoided. They post a warning sign on just about every attraction that moves, however, advising that pregnant women do not ride. I'm pretty sure it's to cover themselves. So I wouldn't do Men In Black and I would have them take the spin off of your cat in the hat vehicle. Unfortunately, Spiderman spins as well...just a few times, but I don't think I'd like to speculate as to how much is TOO much.
I did Kong, Earthquake and Back to the Future as they just jerk you around a bit, the baby is well protected in there and there is no spinning or anything like that. Actually, aside from MIB, I can't think of anything at the Studios that should be a problem. At IOA, I can't think of very many things that won't be, however...
Don't cancel though, go and enjoy your freedom!!!
Drink plenty of fluids and take it slow! 5-6 months is the best time to travel, IMO.
Are you going to WDW at all? They might have more to keep you busy the rest of your stay...perhaps a couple of days over there might be fun.
Have fun!
Karen