According to the Unofficial Guide to WDW 2001 p. 219:
(this woman who did WDW for the book was in her fifth month when she went). These are the only things she couldn't do .
Splash mountain: because of the seat configuration-"your knees are higher than your rear, causing compression on the abdomen (when it is this large). This is potentially harmful to the baby."
Big Thunder Mountain
Mad tea Party (may be okay if you don't spin cups)
Space Mountain
Tomorrowland Speedway- because of rear-ending
Epcot: Body Wars and Test track and all simulator rides
MGM: ToT , Star tours, R'nR, she rode Backlot tour, even though there may be some question about the "earth quake " part.
AK: Dinosaur, Kali (toss up- bouncy and wet). I heard the back seats of the Safari are very bumpy and jerky.
Water parks-all slides off limit, wave pools and floating creeks are great!
Also recommended was a "belly bra".
Stay safe and have fun!!!!!!!