Pregnancies will typically produce single babies, but sometimes it produces Triplets too! To increase the chance of this happening you can purchase the Fertile trait from the Rewards Store or use the cheats for it.
Aside from giving birth to triplets, it is also possible to create a triplets in CAS. The triplets can look:
- completely identical to your main sim
- have different genders than your main sim
- completely different than your main sim, if you click the "Randomize" button or if you edit the sims yourself.
- have a different age than your main sim (This is completely illogical, but it has nothing to do with real-life triplets. If you change the age of one of the triplets, you will simply receive a younger version of the main sim and they will look completely identical to each other when they are the same age.)