Next there's internal rotation, where the fetal shoulders internally rotate by 45 degrees so the widest part of the shoulders are in line with the widest part of the pelvic inlet.
She's come a long way: After feeling intense pain while taking part in her annual cancer walk in Australia last September, the star soon learned it was due to a cancer-induced pelvis fracture.
So here, natural selection found a compromise: mom's pelvis stays narrow enough to walk and run, and babies are born earlier so their noggins don't get stuck.
The investigators discovered that that they could predict exactly where each foot would fall based on the movement of the person's pelvis during the previous step.