Mary Jane became pregnant at the beginning of the Clone Saga. Impending fatherhood was one of the main reasons Peter retired as Spider-Man during that story-line, passing the mantle to Ben Reilly. However, at the end of the story, Mary Jane was poisoned by Alison Mongrain, an agent of the Green Goblin, and the baby was stillborn (or seemed to be, as Mongrain took the infant away with her). The stillbirth of his child, combined with the death of Ben Reilly at the hands of the Green Goblin that same night, prompts Peter to retake the Spider-Man identity.