An "abortive procedure" is not the same thing as an unborn baby dying as a result of a medical procedure intended to save the mother, ie: chemotherapy. Direct abortion (dismembering the child, burning it alive in chemicals etc) is never allowed.
So removing the fetus surgically with minimal trauma before starting the treatment is verboten, but poisoning it with the drugs over a span of weeks until it dies and bleeds out is a-okay? 
Monstrous. 
William made an erroneous statement regarding RC social teaching. I corrected him. Your inability to distinguish between a direct act with an intended consequence and an unintended consequence of an indirect action is your own problem.
No, my problem is that exposing a fetus to chemo will torture it for days, if not weeks, before killing it, and I find the idea that this is more acceptable than an abortion before treatment revolting.
Such a desperate situation needs brutal honesty. Say 'This is my child's life, and I'm going to sacrifice it in order to save the life of its mother'. Then do it quickly. The child deserves that much.
(The RC will disagree, of course. Not that I give a fig.)