I dunno, potentially could have post-birth events, I can literally imagine a few scene with the cast that might resemble something from 3 Men and a Baby... assuming some of you here are old enough to know the film
Yeah, but that is epilogue, her story will be over by then. The idea is that she will be less involved in the other stories, and it will matter less if she is knocked up or not, since she won't be doing as much. Where as now, if pregnancy is an option, he has to make extra versions of each girl, for every scene they can be in, for every stage of the pregnancy. So, unless you keep it very limited to people who are not main girls, that only works in a game that uses layered sprites, like a 2D game. The added workload, game size, and so on would just be insane.
But it's been said here many times, pregnancy will be added for the main girls, but not until their plots are done. That way they can be effectively retired, and he can focus on other things.