I'm not pregnant, but from all the threads about pregnancy that I've read, there's more that pregnant women CAN do than things they CAN'T do.
You've also picked a GREAT time to go. You'll be 7 months pregnant (assuming I counted correctly, which is not always a sure bet!

), and the weather will be nice. Not sweltering, but comfortable.
Just take it easy. Make sure you plan those mid-day breaks in, and keep yourself hydrated - TONS of water!!! You might also consider a wheelchair or
ECV. May seem like a pain, but it might save your feet and back a LOT of trouble. If you have the Unofficial Guide, there's a chapter (or a section at least) devoted to doing Disney while pregnant. If you don't have a copy, why not?!
In the Magic Kingdom, stay away from the mountains, and the tea cups. I would say that everything else is pretty safe.
At Epcot, I'd stay away from Mission Space, and Test Track.
At the Studios, stay away from the Tower of Terror, and the Rock 'n Roller Coaster. I'd ask your doctor about the backlot tour. I don't know if the shakey portion of Catasprohe Canyon would be a good idea.
At Animal Kingdom, unfortunately, the rides are pretty much off limits. I'd say you'd be fine to do all the shows, Tough To Be A Bug, and Triceratop Spin. DEFINITELY not Kali, Dinosaur, or Primeval Whirl. Again, I'd ask my doctor about Kilimanjaro Safaris. It can get pretty bouncy on that one. The good thing though (in my opinion) is most of the "attractions" aren't rides. Those jungle treks are gorgeous, and I could soak up the Animal Kingdom atmosphere for hours.
And once again, that's coming not only from a guy, but one who has never even traveled to Disney World with a pregnant woman.
Good luck, and congratulations!!!!!