I've been playing for about 60 hours, three characters and no babies. I'm assuming either there's something about the game I don't understand like a trait or negative relation making pregnancy impossible(like devious -2) or I have some kind of mod conflict that broke the default pregnancy. The only mods I can think of are if bltweaks has a setting buried or the detailed character creator breaks the age or something (I only changed age on my first character). I just tried the pregnancy control mod which is what you want, you only get pregnant when you use a dialog. But even that doesn't work for me so I think something is pretty broke.