Adding pregnancy in sandbox games is normally a bad idea.
Every reachable scene must be rendered again.
Then all the different outfits, they blow up the work exponentially, and that won't go well for a long time.
Just think of a scene with 3 different girls, that can have 4 different outfits each and be pregnant or not.
That alone would be 24 possibilities to render.
Of course, if you have a strong render rig like a modern threadripper with some RTX2080ti or even Quadro cards and automate this process, it wouldn't be a big problem and some freedom and changes are great, but in doubt I prefer more story/events over another outfit or pregnant versions.