In what cirstances is abortion a better choice?

I saw this clip recently on children in Iraq born with severe deformities and birth defects. It was caused by the devastating nuclear weapon footprint left there by US forces. Some of the parents never want to have children again and even wish they haven't gave birth to thir deformed children in the first place. I was just wondering, if they somehow can inform the parents before delivery that the child will be born of birth defects, is it justifiable to allow them to abort even after 3 months of pregnancy? A more general question would be that if any deformity is so severe that the child must be on constant medical care and undergo tons of surgery every year, is it justifiable or even reasonable to "put down" or allow the baby to die at birth if the mother wishes?