From a simple story perspective, Jill saw no need for taking birth control until she starts dating MC, because she was a virgin before Episode 8. Same with Maya, she was a virgin—and lesbian—so she was also not taking anything by Episode 7. Contrast that with Josy, in the same episode she says she's been taking pills so now it's safe to creampie her. That makes her desire for MC to fill her up back in Episode 2 highly suspect though (unless you get conspiratorial and think she was preparing herself to be ready for when she finally cheats on Maya with MC).
It really doesn't matter, outside of Nora and Arieth pregnancy is a non-issue. If it's going to factor into MC's personal story, it'll probably be a scripted event towards the end of the game.