well, I'm pregnant right now, and so I'm still trying to decide what to do. my partner and I want to raise the child in Canada, but I haven't decided yet whether to go back fairly soon, so I can be covered by BC's Medical Services Plan by the time the baby is due (in January), or to wait and then bring the baby as a permanent resident. Both have significant negatives -- if I stay, with my partner in the US, then it will be more difficult to get the paperwork filed, and we'll have to move with a newborn. If I leave now, then we have to be apart during my pregnancy, and figure out how to ensure we are together for the birth of the child and its infancy. Right now we are hoping to finish our application for my partner's sponsorship and get it submitted as quickly as possible, so that there is a chance that, whether I return to Canada early or not, we can both be in Canada legally and safely by the time the baby comes.
There may indeed be exceptions for birth of children abroad to Canadian citizens deployed in the canadian military, but I don't know about that.