Okay two options for the many codenamed Kitty Pryde.
Well for Kitty there is one obvious one, in an infamous 3 arc 2012 story, Kitty became infected with Brood, giving her the appearence of a pregnant woman. The X-Men minituraise themselves, go inside her and clear out the brood, and when they do that Kitty reverts to the slim figure she normally has... but what if she didn't what if, instead, after her allies clear out the infection, Kitty finds herself, for reasons no one can deduce, still stuck looking heavily pregnant. Can she find a cure, or even why she's stuck like this in the first place, or is  this her fate forevr?
Not interested in thias idea, okay, how about this: 18-year-old Kitty Pryde is kidnapped by Mr Sinister. When she is brought before him he explains why; having studied Weapon Plus' files of a project X-23, which proved that clones grow healthiest if incubated in a human womb, instead of an artificial incubator. He has also noted that, as her intangibility powers should allow for painless labour, or even a ceserian without cutting her open, not to mention theoretically allowing easy access in utero, Kitty would make a perfect surrogate for his projects.
Of course he isn't content with 'stock', and sets about modifying the girl; altering her hormones so that her body thinks it's in a state of perpetual pregnancy, altering her breasts to promote heavy milk production (Sinister's nutrition feed for his clones has breast milk as it's base, might as well use his incubator to make that as well), and permenantly malforming her womb to ensure that at it's smallest state she already looks heavily pregnant, so there is pleanty of space to put his projects.
The X-Men rescue her, of course, but not before these irriversable modifications have been made. How will Kitty adjust to her new body, and did the X-Men really save her before Sinister put one of his projects in her?