Hi Amanda!
Congratulations on the new baby! How exciting!!
First, the best thing to do will be to check with your physician before your vacation begins. Be sure to ask about any restrictions or types of ride movements that you might want to avoid. They will have the best advice for your particular situation.
Before you go, you can also check out the different attractions pages at each park. For example, for
Big Thunder Mountain Railroad at the Magic Kingdom, does have an indication on its page that "expectant mothers should not ride". These restrictions will also be listed outside each ride at the parks.
As always, be sure to make sure to stay hydrated and plan plenty of rest breaks!
Hope you have a great time!