To make a ghost baby, develop a relationship with a ghost as a female Sim and get the ghost to ‘Try for Baby’ with them. There will be no father in the family tree as though it were an immaculate conception. With males, you’ll need to make the ghost playable via the science lab opportunity. There is a 50/50 shot of getting a ghost baby instead of a normal Sim baby when they try this way. There isn’t any major difference between a ghost baby and a normal Sim baby, but some people want them because they look cool.