An abortion is not “taking off of life support.” it involves active killing, like injecting poison into an IV tube.
The distinction is more slippery than it seems. If the method used was to induce the woman to deliver right now, at 4 months, that would be "removal of life support" - the uterus.
So you use a different kind of poison, one that hurts the woman less than the fetus but does her no good physically. Intent matters. You aim to kill. This is hardly different from exposing a new born infant.