Anything to do with the usual "extreme" fetishes - gore, scat, pissing, rape, et cetera, are obviously big turn-offs for me in any pornographic content, preg or otherwise. I like my women alive, thank you very much. Also, consent is sexy.
Another thing I dislike in pregnancy-related content specifically is anything to do with abortion. I'm not like, a pro-lifer or anything like that, but I still don't think abortions should be outright fetishized like that. It just feels wrong, man.