Random NPC's will only get pregnant if their fertility etc is correct and they have sex. This will not happen unless the player is in the same cell. Pregnancy progress should catch up though if you leave the cell and come back a week/month later.
Alright but i've yet to find a npc that's pregnant and i got setting 4 on. I'm not sure how it works do they need to have sex or not to have a ova and end up preg. I'm not sure what settings are best for npcs to be effected so let me know what i need to change.
To get too many random NPC's pregnant will mean a lagfest too.