Hi and CONGRATULATIONS on your pregnancy!
I have been to WDW twice whilst pregnant (though at a later stage than you) I was around 20 weeks both times. As you probably know, the first trimester is the most "at risk" part of your pregnancy, however this doesnt mean there arent TONS of things you can do and have a fantastic time.
As far as rides go, Disney list each attraction in the Park Guide / Map and its suitability for certain persons. Obvious rides to avoid are coasters, TOT and anything with a drop like Splash Mountain or jerky movement like Dinosaur or Test Track. There are a few which, even though Disney recommend a pregnant lady shouldnt ride, I did so. These were Kilimanjaro Safari and Kali River Rapids. The reason I rode these, was I am familiar with both and didnt feel they posed a threat to my health. Had I have been in the first Trimester though, I probably wouldnt have ridden even those.
Things you can enjoy are the parades, the shows (like Philharmagic and The Muppets 3D), gentle attractions like Peter Pan, Dumbo etc, plus all the usual character meets and shopping
I never felt I was missing out visiting WDW whilst pregnant, there was plenty to keep me amused! I would recommend frequent stops and to drink plenty of water, as you will feel much more tired than usual. If you are driving to the park, tell the attendant you are pregnant and they will often let you park nearer the gate. Make a mental note of where the First Aid center is in each park in case you feel unwell. Here in the UK, our obstetricians recommend carrying our maternity notes on us whilst away from home, so it maybe worth taking them with you (not nessacarily into the parks, but left at your resort).
Have a fantastic trip and once again, CONGRATS!!
Allie