I had a female Sim get pregnant and I switched over to another household and when I returned the female Sim had given birth. I have auto-aging turned off and only aging is allowed in the active househ...
Myself I can't seem to knock up sims that are computer controlled, or they don't show like other sims. One of the town sims comes over every day and we try for baby but nothing seems to happen. His wife don't seem to care that this happens I guess she is quiet