This just came up in another discussion, and we don't seem to have a thread about it.

First, I'll go with the argument that the reader is meant to understand that Mary Jane is pregnant in One More Day.

The final chapter of One More Day began with Mary Jane standing by a bathroom, shortly after Mephisto offered to save Aunt May’s life in exchange for Peter Parker’s marriage. Some readers came to the conclusion that Mary Jane was throwing up, although this is not explicitly stated at any point.



After Peter and Mary Jane accepted the deal, Mephisto gloated and showed them a vision of the daughter they would have made if they had just stayed married.



This was seeded in the preceding chapter, in which Spider-Man met a cryptic little girl and a cross-dressing Mephisto. It may be an understatement to say that this foreshadowed the later scene, considering how obvious the dialogue is. It was pretty clear what JMS and Quesada were setting up—in a scene in which a little red-headed girl, described as a possibility Mephisto doesn’t want to talk about yet—talks about her beautiful mother, and smart father.

Comics is a medium which is heavily reliant on visual shorthand, and a young woman possibly throwing up is visual shorthand for morning sickness. This is also a story that ends with the revelation about the child Mary Jane could have had.

Rob Bricken of Topless Robot was clearly under the impression that this was a plot point. In his rundown of the worst non-Clone Saga Spider-Man stories, he summed up One More Day as Spider-man Sells His Pregnant Supermodel Wife to the Devil. He elaborates the point…

Around part three of One More Day, Peter starts having weird encounters with other-dimensional versions of himself that are wealthy but alone and miserable. They lead him to a little girl who bitches at him for being horrible and self-centered, and then takes him to Mephisto. Being the Devil and all, Mephisto promises he could save Aunt May, but only in exchange for the most valuable thing Peter has: his marriage! Mephisto then teleports Spider-man back to wherever the hell MJ is, and it turns out she got the same offer. MJ is having obvious morning sickness, but talks things out with Peter anyway. She decides giving their marriage to the devil is okay because, hey, they’ll probably find each other again (I read it as “we both know this **** won’t stand once there’s been a change in editorial”). Mephisto makes sure Peter knows that by making the deal he’s essentially giving Mary Jane a magical abortion and shows them the daughter he’ll never have, the little red-haired girl who yelled at him