aww sad message

I've seen that happen in my game as well, and I was not happy about it, because they were one of my families that I rotated with. What happened was one of the pets also got pregnant and thus the game decided to end the human pregnancy, because of the 8 sim limit. I was so upset that I just stopped playing that game save (yes I know I could have backed up before it all happened, but I was that upset). Since then, I just make sure that I don't allow them to have more than two pets. My game is already set not to allow more than 2 children to be born to the family, not per pregnancy, but total number through a sim's lifetime.