Our DS is just 2 and we are going on his 3rd trip to WDW next week. His first (out of me that is -went twice while pg too) was when he was 8 months old. He actually was an awesome baby on that trip, and I wouldn't let it hinder you in going to bring an infant. Just needs a bit more logistical planning, that's all. We stayed at BWV, and got a one bedroom with a full kitchen. I really liked that option as I could have formula in the fridge at all times, and have baby food/cereal stocked. We took slower mornings to get all up and fed and relaxed and then meandered to parks. WE asked for a high chair in the room so he could sit up at table etc, and he loved to play at the coffee table in the LR too- he was just learning to stand while holding on to something. Just bring some floor toys, or maybe if you can squish one of those soft floor play gym things in the bag to keep him/her occupied for a while. He totally napped in the stroller, and some days i would camp out in the Baby care stations at the parks where it was nice and air conditioned and let him sleep there. The baby stations are all nicely equipped and they have supplies on hand for purchase if you forget anything or run out of diapers etc. They have private nursing rooms too. The one at AK is best in my opinion.
Anyway, hope you have an awesome trip when the time comes, and hope everything in your pregnancy goes smoothly!!
Jen