Holy crap is this relevant to my interests. Holy crap do I have a kink for I Didn't Know I Was Mpreg. Even if nobody writes this please just tell me all your thoughts/imaginings on this matter. I assume you've read Yield by PhantomsDaughter13? In that one Bucky does know what's up but Steve doesn't so it may be at least peripherally good for you (and her stuff is some of the best mpreg I've ever seen).