Ok ill sort this out. I have ben trying to figure this out ever since the Sims 2 came out, and i think i have the answer. In the alien race, MALES are the ones that get pregnant, not the females. And if you are saying that ur alien wife had a baby to, it is because of the game genetics. Almost all females in the game have babies when they woohoo. But it is also in the game genetics that if a man woohoos with an alien woman, then he will have a baby because in the alien race men have babies not the women.