Yeah, gonna add, codingwise it's possible to make (RNG for impregnation after submissive sex event, timer, status effects due to pregnancy, then when timer hits 0 an event occurs where birth happens), but m-preg is pretty niche in games and, given it's a mostly male game (I mean, it could change, who knows), I doubt they'll add female pregnancy given it'd be for a very specific subset of players. Unless it's oviposition, I suppose, given you could add that as "eggs go in during sex, creature leaves, eggs pop out of hole, you leave", but that's not really pregnancy.
Anyone into it would probably be better looking for a third party to mod the game with altered code. (Not me, though. I might understand how to do it, but theory and practice are very different things with python).