We went when I was 32 weeks pregnant with my OBGYN blessing (he said he took his wife when she was 34 weeks pregnant, but then she had a Dr. with her!!!
) I was really sick most of the pregnancy, but felt the best from 6 to 8 months. (baby was fine, I just couldn't eat.) Our trip was early Feburay and is was cool, I was sad about that but I helped, no swelling or any troubles of any kind. Infact I felt the best that week just getting away to my very favorite place of all time and dreaming about how fun it will be to share it with my child later. (I also was very "small" for someone that far along, it wasn't until after that I "popped out!" Staff was really nice to us and gave us a room with minimal walking distance.
I would consider it if you can if you can cancel up to a month before with no consequnces, if not wait until later. A month before you should have a good idea how the pregancy is going and if you are up to it.
Also what time around Christmas? Before the 20th is pretty low crowds, but it can be crazy after that. We took DD the next year (Dec 2001) when she was 8 months old and had a blast, but it was Dec 13 to 20th. I really recomend that if you can.
You won't be the only pregant women there, but far. Infact on the plane ride home there were 3 other VERY pregnant women, one with twins!
Good luck and congradulations!!!!