Pregnant Men | The Sims 3 Same Sex Pregnancy Mod
The Sims 3 is a strange beast morally speaking. On the one hand, it seems designed to follow natural biological laws, and on the other it seems to make moral judgments aimed at not annoying portions of its user base.
The base game will not allow female / female couples to conceive a child, nor will it allow male / male couples to conceive a child, as would make logical sense if the Sims 3 universe were biologically driven and not digitally driven.
However, if we're going to follow the laws of biological certainty, then it makes sense that adults and teens should be able to procreate. After all, up until a few hundred years ago, a girl was an old maid if she hadn't been married off by the time she was 16 or so. However the Sims 3 allows absolutely no serious romantic relationships between adults and teens and it certainly doesn't allow for procreation. On the plus progressive side, in the Sims 3, same sex couples can get married without the rest of the town descending on City Hall with badly spelled protest signs. Come to think of it, the Sims 3 is blissfully absent of anything that looks remotely like religion, which might also be why it's entirely absent of war and largely absent of violence.
Fortunately for those of us not content with the restrictions of the base game, there are mods out there that allow anything to happen. If you're a fan of creating same sex sim couples but have always been vaguely annoyed that you couldn't make them procreate, then the Autonomous Romantic Socials mod is for you.
It allows not only same sex pregnancies but a range of other interactions, and by using it your sims will interact romantically without you prodding them continuously to do so. (Before using this mod I used to spend many teeth grindingly annoying minutes forcing sims to interact romantically in various ways in order for the 'Try For Baby' option to come up, only for one of them to get hungry or sleepy or wander off and stare at a wall instead of getting the business done.)
Of course, if you are going to go the same sex route with male sims or teen sims, you'll need to download new sets of clothes if your sims aren't simply going to be floating heads for the duration of their pregnancies.