My last post wasn't very constructive, so I'm adding to it. I can send you my newest save/rotation. I have a family of 4 sisters, I made each one become a different occult and had them live together until they married out or had enough money to move to their respective occult town. The oldest sister, Meg, is family oriented. I switched to the second oldest, Jo, shortly after Meg's baby aged up to a toddler. Meg called almost every day asking if she should have a baby. I picked the middle answer, decide for yourself because I've had the most luck with this one not ending up with a pregnancy. On the last call, she became pregnant. I didn't know this until I switched over to the third sister, Beth, and invited all of her sisters over. In comes Meg, very pregnant. As soon as she has the baby, Meg calls Beth, again asking about having a baby. I'm about ready to fully edit mode her and make her incapable of becoming pregnant; the sims equivalent of tube tied.
I'm pretty sure this can be duplicated as this is now the second save I have had it happen to. The only mod I ever used was the spaceship one to fix the fairs breaking the spaceship building, which I was able to delete earlier this month. To recreate:
Create 2 families, the only restriction is that the female sim in one must be family-oriented. It is up to you whether you want to play her long enough to marry her off or if you want to start her off married. I don't know if gender or the ability to impregnate of the spouse matter, but if it doesn't, it should. I currently have neighborhood stories turned off since I also have aging for non-played sims off until I get back to Meg's household, so I don't think neighborhood stories matter; they are both played households anyway. Have a sim in the second family befriend the female sim that is family-oriented in the first family. Play the second family. The female sim in the first family should start calling her friend in the second family asking about trying for a baby before a week is out.