I went in my first trimester, and here are my suggestions:
That adorable bag for carrying milk/formula for your bundle: break it in by keeping some electrolyte water for yourself!
Don't try to park hop.
Find those long slow attractions that people often avoid: they are perfect for a rest if you don't want to go back to you room:
MK-Country Bears/Carousel of Progress/Pirates (NOT BORING-just long and cool)/Hall of Presidents/Small World
EPCOT-Ellen's Energy.../Spaceship Earth/America Pavilion/France Film/Canada Film
Animal Kingdon-Festival of the Lion King and Nemo Show
DHS-Great Movie Ride/Muppets/Little Mermaid
Carry lightly salted Almonds, if you are not allergic.
Each park has a Baby Care Center...find out where they are when entering a park. Should you need it, they will provide a comfortable place to rest, and they are near first aid.
* If a cast member tells you that a ride is merely a simulator, so you need not worry about riding, don't believe it! (I rode Star Tours with that advice, and was nervous for the next 6 1/2 months!)
Have a wonderful time, and don't be surprised when your child is born a Disney addict! (My DD16 is!)
