My first experience with someone having to make a decision regarding a 3rd trimester abortion was on my 3rd year OB gyn rotation as a med student. A 30ish mom with a 9 yo and a toddler was diagnosed with a very aggressive form of breast cancer that initial staging showed was in the local lymph nodes at least. She was 6 weeks or more from her baby being at the brink of viability (months in NICU, likely lifelong GI issues, possible cognitive deficits, etc). To have even a 50-50 chance at 5 year survival, the heme-onc team said she needed immediate chemotherapy which meant terminating the pregnancy.
Keep her baby and not live to see any of her children grow up. Abort her baby and have a 50% chance of being there for the other 2 children. She chose to keep the baby. Don't know how it turned out but I have a pretty good idea.
Almost all late stage abortions are true life or death situations for the mom, or fatal birth defects for the baby. These are devastatingly difficult decisions, and most of the parents consider it no different than the loss of a child.