In the super intense birth scene in breaking dawn, Kristen Stewart looked almost unrecognizable! They made her look as if she was about to die.
So how did they get her to look this way? Using lots of makeup and a bit of movie magic.
For the makeup, they were actually inspired by "thin fashion and runway models with very defined jawas and cheekbones."
So Kristen wore makeup that exaggerated all her bones, especially her cheek, chin, and collar bones. They added a bit of "post production" work too (which means computer editing). She looks painfully thin in the birth scene.
Source: Hollywood Life