Unfortunately, exceptions for the LIFE of the mother are very different than exceptions for the HEALTH of the mother. "Health" of the mother can and does include "mental health", which opens up a whole 'nother avenue.
PBA's, [as heard from those who perform them (Tiller, et al)], are often performed on girls/women who "don't want a kid right now/can't afford it/forgot, again", and very rarely on those whose pregnancies are "at risk", either by fetal abnormality or risking the life of the mother.
With regard to the health of the mother issue, I agree that it's very uncommon. I'm sticking to my guns that the example mentioned above is a good reason to keep reasonable protections for mom in the law. Not the recommendations that Pelosi, et al made, but reasonable protections.
Also, I'm sticking to my point about fetal abnormality being a significant reason for a very large number of late-term abortions. Most non-invasive anomoly screenings, such as ultrasound aren't done until 18-22 weeks. Again, I'm not saying that it's right, I'm saying that it's a major factor.