The only justification for an abortion is the life threatening condition called ectopic pregnancy which can cause blood vessels to burst and the mother can bleed to death.
This is only the case because the baby will die anyway with the mother if there was not any way to save both.
In this case the decision is justified not by the decision to take a life of a child, but that of favoring the reduction of two death’s to one death is preferable.
There are very very few ectopic pregnancies like that, but they do happen.