They could easily add pregnancy to the game by tying it to the alchemist boss of the 2nd level. This is how it could be done without messing with the story too much:
After he is defeated the alchemist could ask Karryn to test a few potions for him and he could offer her money for each potion that she tests and and of course he would promise that it is completely safe. He would tell Karryn that he needs a woman to test it, for whatever reason, and since she is the only one in the entire prison clearly she has to help him. The first potion he has her test makes Karryn able to get pregnant from men, maybe the reason she can't be knocked up is because she has some kind of birth control method like enchantment or whatever. The first potion breaks that. Of course he doesn't tell Karryn that. Then the second potion he has her test would make her able to get pregnant from non-humans, like goblins. The third potion could be one that speeds up her pregnancies to happen over a matter of days, he could even offer to pay Karryn for any children she has, after all he always needs more test subjects. Also, the alchemist could offer to set up a breast milk pump for her in the infirmary (could be an edict) that lets her make a little extra coin by selling her breast milk to the inmates.