The theory is based on not only the vile sexual abuse Sansa suffered from her late husband, but Ramsay's last words — "You can't kill me. I'm part of you now" — audible in this video clip:
Ser Davos Seaworth (a.k.a. Liam Cunningham) doesn't think this theory holds water, telling TV Guide that Ramsay can't possibly know whether Sansa is pregnant or not:
"Unless he’s got one of those 'Game of Thrones' pregnancy sticks, he’s not gonna know. I would imagine it’s open to whatever you want it to be, but I think he’s saying he’s put himself into her head. That’s what I took from it. She’s never gonna get rid of him because of what he’s done to her. He knows what he’s done to her. It was off camera, what he was doing to her, but we all know what it was. But I think he’s placed himself in her soul for all the wrong reasons."
Of course, there's the quote that could be read as Sansa's biological intuition to contend with, too. When Sansa described her Ramsay-related PTSD to Littlefinger, she said, "I can still feel it. I can still feel what he did, in my body, standing here, right now." Could she be saying she kinda senses a baby Bolton, or is it just a damned metaphor?
Game of Thrones fan(atic) site Watchers on the Wall also pour a vat of Flea Bottom slops all over the pregnant Sansa theory:
I am enormously happy to report that Watchers on the Wall can put a certain “theory” to bed. If any in our readership believed a certain insistent rumor, the following may be a relief to hear: Sansa will NOT be (or get) pregnant in Season 7.
Good, I guess? Personally, I'm not averse to seeing characters I love suffer as long as it's good for the storyline. Obviously Sansa has had an unbelievably shitty time throughout Game of Thrones, and her trauma could logically alter her path: Will she become a villain, form a partnership with Littlefinger or just full-on DIE?
Damn girl, just don't get pregnant — that never goes well for Starks...