If your Sim “discuss expending family” with a Love interest it can happen that you have a miracle pregnancy. The game doesn’t filter played sims and unplayed sims. It’s the same bug/feature as the ring in the bag scenario just you don’t have the call.
More have this problem, especially in reddit/sims4 you can read this often. 83Bienchen have made a mod (Autonomy Mods -> neighborhoodstories), if you use mods I would recommended to use her mod until the team fix all this bugs/feature with played sims and story progress. If you don’t use mods, just dont use this social interaction.
