15LOSES BABY WHEN PREGNANT MARY JANE IS POISONED
This one's a real bummer. In Sensational Spider-Man #11, Peter and Mary Jane Watson reconcile and decide to give their relationship a real shot. They get married, and later, MJ gives him the big news they are going to be parents. But she worries about Peter
continuing to be Spider-Man, putting himself in danger when they are starting a family. That's when Peter decides to quit and hands over the reins to clone Ben Reilly. But when Marvel editors ended up deciding to bring Peter back as Spider-Man, they had to somehow resolve the baby situation.
So, Norman Osborn aka Green Goblin hires a mysterious woman to pose as a waitress at the Daily Grind. The woman poisons pregnant MJ's food, which causes her to go into premature labor. After an agonizing delivery, the doctor breaks the news that the baby, a girl, didn't make it. The comics sort of make it seem like maybe the baby didn't actually die but is stolen by the evil woman and brought to Osborn as yet another way to mess with Peter, but it's never fully explained exactly what happened to the kid. In some arcs, however, the little one became Spider-Girl.