Specific fic: mpeg!Dean and Wincest
The story I'm looking for was about Dean unexpectedly getting pregnant. He already had a lot on his plate with keeping Sam from scratching at that wall in his head. I think they decided to settle down in Sioux Fall.
I think they found out that the baby was a girl and decided to name her Mary. As they were out celebrating that they'd decided on a name, Dean went into labor at the restaurant. They started driving home (or to Bobby's), but things were progressing really fast and Sam had to pull over. Cas showed up, but decided that it was too late to move Dean, so he ended up giving birth in the Impala.
That's all I remember, plot wise. I know I read it on AO3 a couple of years ago and I think it was about ten chapters long. I can't find it anywhere and I'd really like to read it again. Please help!