I'm not sure how you could handle "optional" pregnancy in a more linear game like this where all the characters know each other. Any "optional" pregnancy would have huge ramifications for the storyline and necessitate two wildly different narrative branches that would be way too much for anyone to handle.
I think the dev has said not to expect pregnancy. For those of us into the stuff though I'm glad there have been some lines of dialogue thrown in there, girls talking about wanting your babies and such. I'm kinda hoping some of the "purity routes" contain pregnancy, at least their endings, but that's so far down the line I doubt it's worth speculating about at the moment.
