I have been to WDW twice pregnant, in 2 different pregnacys (and one trip to VB just last month.)
1st time Feb 2001, I was 32 weeks (the same as I am right now on my second pregancy!) I felt really good and all went well. However I don't think I would want to be there right now weather wise. Otherwise I think I could handle it.
Second trip I found out the month before we left. I was 8 weeks for the trip. All day sickenss started a few weeks before we left and I had alfuwl sickness my 1st pregancy, so I talked to my Dr. about it. He took pitty on me and gave me prescrition Zofran. I was unsure at 1st, but it really helped me to feel better. However when at WDW with all the magic, exersize, good food and fresh air (it was early Jan 2004) I felt great. (when I got home it was another story, sick until well after 17 weeks.) To make maters more funny my friend who went with us just found out she was pregnant the day she left to go there (she was 4 weeks for the trip.) Keep eating, small snacks, even when you don't feel well, it helps. I needed the Zofran until at least week 16 or so. (But at 32 weeks I currenlty feel good, uncomfortable, but what can you expect.)
This past May we took our summer vacation to Vero Beach, but didn't do WDW. I was mid 6th month almost 7. I felt great, the best of the whole pregancy. For me going on vacation makes me feel better, infact I told my husband I was actually enjoying being pregant (I don't make a "happy" pregant lady.) 6th month can be a great time for a trip, 7th isn't too bad either (if it is near the start of the month.) It really was a great trip (I recomend Disney's DVC Vero Beach to anyone especaily familes with young children and pregnant women!)
Leave yourself an out so you can cancel if you need to, but I would go for it (and did) Also try to get in to see your Dr. before you leave for the trip. Ask him about the med if you are feeling sick, it really does help. My doc told me I could ride any ride I felt like in the 1st trimester, I did Dino, Mission Space and the safari ride at AK, along with all the ones my 3 year old DD could go on too. No problems at all. Don't do any slides on the water park where you go in feet 1st. (with out a raft.) I didn't miss riding the thrill rides at all, at the later stages you don't want to be moving like that! Keep your exersize up for the later trip so you will be able to make it, but don't push yourself in any way.
Have a great time and congradulations!