Not sure what's going on but replaying the scenes in the cg room doesn't seem to be impregnating. Am I missing something? I tried for a while now with no results. It seems like it only works during normal gameplay after I save scumed an attempt.
It's a random chance to happen, which is lower or higher for some characters. You might just be unlucky. The exeption are main characters, which always have a choice during their scene, and a 100% chance to get pregnant if you go for it.