@Saamok
well, that depends. My mom was a neonatal nurse, in situations like these where the mother was warned the pregnancy could jeopardize her own life beforehand and she (in sound mind) chooses to prioritize the baby, the doctors can honor the mother's wishes. I'm sure there's paperwork to fill out beforehand, but it's really not much different in theory than a DNR request.
Now if complications just occur randomly without the mother being able to express her desires on the matter, they of course will prioritize the mother.