How much danger? How immediate?

What’s the line between medical necessity and medical advisability? When do things become a necessity? Take something like the water breaking at 17 weeks. Is an abortion an immediate medical necessity even though the woman’s life isn’t yet in immediate danger?

What happens to doctors when courts decide that they fell on the wrong side of that line?

The problem with things like this is that drawing the line badly or fuzzily and medical mistakes lead to women dying. Abortion was legalized in Ireland after one mistake like that, when doctors didn’t want to violate the ill-specified law and erred on the side of intervening too late. The mother died.