Congrats! DW is pregnant, and we were trying for FIVE YEARS. So I know where you're coming from.
I've researched this heavily, both here and other boards, all over the internet, and any Disney Book I could get my hands on. I wrote DW's travel plans, showed them to the OB, and she approved. IT's a very short list:
A) Disney has rides marked as not for pregnant women (and usually people with heart conditions, bad backs, etc). Don't ride them, even if it seems silly. Why risk it?
B) Drink water
BB) Drink water.
BBB) Drink water. Enough said.
C) This is one trip not to commando tour. Take a leisurly pace. If DW's tired, we sit. If she's hot, we get in air conditioning. If she want's to go back to the hotel, we go. End of story.
D) Relax, take it slow, and enjoy! Our OB said if we follow the above rules, then a Disney trip is incredible, because a happy mother passes that feeling on to the unborn child, and the walking is good. We'll be in month six! It just seems like the rule is don't ride anything dumb, don't let your radiator get low, and take it slow and cool!
Congrats again. Enjoy Disney.
Pat