In Part 20: Impregnate, Lifesimmer installed the Hospital Overhaul Mod. This mod allows sims to: get impregnated, arrange surrogate pregnancies, donate sperm or eggs, have abortions and get ultrasounds. Trey donated his sperm to the hospital and Mariah got impregnated by it, unknowing of the donor's identity. Despite that the impregnation took the whole part, it was successful. Mariah was pregnant with Unborn Baby Swan.
Owing to the nature of Mariah's failed pregnancy, it can be argued that Unborn Baby Swan did not die, but simply stopped existing, or even that they never did exist.
- Unborn Baby Swan is similar to Unborn Baby Monty from The Sims 2. However, the genetics system in The Sims 2 means that we can predict Unborn Baby Monty's appearance, whereas Unborn Baby Swan's appearance is down to speculation.
- It can be inferred that Unborn Baby Swan would have had black hair, like both of their parents, but they could have mutated brown hair like Owen Doran. Unborn Baby Swan is also likely to have been medium-skinned like their siblings: Owen, Nathan and Charlotte.