Hi Maureen!
Congratulations on expecting your bundle of joy! This must be such an exciting time for you, between visiting Walt Disney World with your four year old and getting ready for your baby. My husband and I went to Walt Disney World when I was pregnant with my son, albeit I wasn't as far along as you will be, and we had a blast.
I definitely suggest sticking to the attractions that don't have a lot of movement, such as
Mickey's PhilharMagic,
Carousel of Progress and
Under the Sea Journey of Little Mermaid. Make note of the attractions that are safe to ride during pregnancy. You will notice a warning at the front of the attraction that says, "Expectant mothers should not ride" for any attractions that are not recommended. Test Track is one you should avoid while pregnant.
You will also want to take plenty of sitting down breaks throughout the day and drink lots of water.
Since you are staying at
Polynesian, you will be right on the monorail line for Magic Kingdom. This is great because you won't have to walk long distances and you can get to the park quickly. You are also close enough to go back to the resort for a nap midday.
I hope you have a magical vacation!
Magically,
Stacy