Dogs and Pregnancy


what's the best way to introduce dog and baby ? I have a very calm 2 1/2 y/o pitbull and a very energetic 1 1/2 y/o bulldog. right now they follow me everywhere and are right by me when I'm sitting down. I've read that dogs can sense pregnancy. I just don't know how to get them prepared for the change even before the baby arrives. is there a book or something lol