Except, there doesn't. It's a made up world that can do as it pleases.Without elements like pregnancy I really don't see the point. There has to be a consequence for getting raped.
No game has to cater to such a niche fetish. I'm not sure what's so exciting about fantasizing about a small child inside of the thing that just got raped. Unless it's simply the child aspect that turns you on.
Very few people wanna see a bloated whale running around giving birth all the time.
I'd recommend The Last Barbarian if you're wanting fat chicks running around. It can offer you an egg in this trying time.