My Sim won't give birth!

My Sim won't give birth. Furthermore, they won't propose or try for baby. I had to impregnate my Sim using cheats, which only works when I force labor. I'm not aware of any other issues involving actions, but I'm sure there're more.
When my Sim went into labor, they went along with the birth normally, going to the crib and all. They acted like they were birthing, i.e. heavy breathing, holding the stomach, but nothing happened. It's like they were reset. When they were reset, they were no longer pregnant, and their stomach was flat again.