If you are healthy and have no reason not to, I think it's certainly doable. My grandmother had my aunt at 45, and that was almost 50 years ago. We've come a long way since then. There are more risks, so it's not an easy decision.
As far as school goes, I got my MBA while Julian was still a toddler. That is also doable.
You know, more than anyone else, what you are capable of. If you have 100% support from your fiancée', that is a big plus!
Best of luck to you all!