No, it's not "what it boils down to", the mother's health does come before and undeveloped fetus, and it should.
Of course it does... As does every consideration where human life is at risk.
The problem is that you on the pro-"Choice" side want to limit the scope of that chain of moral absolutes... so that it doesn't gore your ox.
The reason that the mother's life is priority is that the mother is the superior life, it is established and it is carrying the child... Mother has conceived that child... she did so through her own willful behavior... SHE took action to conceive the child. Therefore the Mother is the vessel, endowed by God with the right to her life, with that come the responsibilities which extend out from there... conception being but one of many.
The Child is dependent upon the Mother for its life. It is also the new life introduced, thus is junior to the Mother.
Surely no one disagrees so far.
Taking a human life requires as its first element of justification, that the life being questioned is a threat to another's life... Where the child's life threatens ANY other life, it's own right to its own life is forfeited.
Now, from that level we travel to the next, which is intent... is the life at issue reasonably recognized as being in clear intent to injure another? If so... "Flip the switch". Instant justification. All Lights are green.
If not... is there any other option to avoid taking its life? And so on...
Such is the tiered construct of justification and choices, standards, rules, statutes etc, for all of Western Jurisprudence down to the simple summons.
You guys just want to set aside that when a woman willfully engages in the behavior that CAUSES CONCEPTION... that
'she just screwed up a little' , when she conceives and needs to kill that life, because if she doesn't she's going to be seriously inconvenienced.
Mom's got a right to save her own life and part of that threshold is that the baby existence is a threat to mommies' life... by virtue that it EXISTS. You want to treat the baby is if it were to be growing in Daddy's body, decidedly unsuited to such, which would in FACT be fatal... which is NOT true in the case of a female.
DO major medical crises come up when that tragic decision needs to be made? Of course... And are their very specific thresholds which establish what IS and is NOT a a true medical crisis? Yep... (See, where this is going?)
Those circumstances are VERY RARE... And few people of reason have ever protested such as they recognize that in nearly every ONE of those exceedingly rare the parents are put in a tragic position of having to destroy something they loved very much.
THAT is not what is at issue and it is deceitful to suggest that it is.