(The info is going towards an Alpha/Beta/Omega verse with a lot of twisting and world building...)
The story takes place in a modern setting. Prior to the current events a mysterious "illness" passed most of the human population and there have been changes. (The changes are still going on, slowly, so what happens at this point is physiologically a work-in-progress, not a finished product - whatever the finished product may be.)
To the actual question:
The basic idea is that even in the verse, men should not be getting pregnant - it's a mistake, and thusly their bodies are only half-way prepared for it. But, if and when they do get pregnant, what kind of problems might there be?
I've been trying to find facts on why men would not be able to carry out a pregnancy (skipping the obvious reason of missing equipment - that is being bypassed in the story). I'm looking for less obvious things, like the strength of a male heart versus that of a woman (a friend of mine thought she saw it somewhere that a man's heart could not pump enough blood for both him and the baby, plus my MC already has heart issues so that will be a problem). What about other organs? How good are they at re-arranging themselves to make room for a growing baby? (No actual births are taking place at this point so the beginning months/first half of a pregnancy is targeted by this question...)
Used search words have ranged from "male physiology", "male pregnancy" to "why men can't get pregnant" and just about every variation I've managed to think of to bring up a response from Google.