First off congratulations. Fabulous news.
I was about three months pregnant in the middle of august 08'.
Stay hydrated, find shade when and if possible and enjoy the slower things and relaxing things Disney has to offer. I remember riding the People mover several times in a row while my sister and my husband enjoyed Space Mountain.....
Still i have to say it was a fabulous time, and we were able to see a lot of things we probably otherwise would not have.