After I had left my doctor sim few years ago, I've give a chance for my new sim. I had waited for 6 sim weeks but got no baby that time.
I play my game in german so I'll try to expain my solution but can't tell you things exactly.
I'm playing at longest lifespan option. I've change my sims' lifespans from long to short and than normal. I think other than the normal lifespan (didnt play short for a long time) pregnant lady wont show.
You shoud aware of that, there can be only 1 special event for a work day ( fainted person or house visit or pregnant lady....) if you get one, you cant get other that day
also you should turn on: automatical age for unplayed house too.
and for last you shoud enable neighbor stories (?) on the menage the world map for all sims. Under that tab there is an option for baby making. Most players are playing more than one household on same map and did not want them to age or marry or etc so they had turned these options off.
After I changed my sims lifestan to normal , and enabling neighborstories enable for all, I got my pregnant patient at second work day.
I hope thats work for you all too.