Question: What is the depth of the pregnancy system?
Well, just another fetish: X% of getting pregnant -> pregnancy lasts a week -> after a few days you can have sex with the pregnant girl with her full belly -> she has the baby -> loop.
Maria explains where the children go when they are born. Plus there is a penalty of not being able to do quests/tasks if a girl is pregnant. The fetish is optional like the rest, obviously.
PS: All this is explained in more detail ingame.