A baby that will certainly die at birth, or likely cause death to the mother, is one thing.

A perfectly healthy baby 1 day before birth that is put to death is entirely different. There is nothing magical about birth that makes it OK to slit the throat of a healthy baby.

As a thought experiment, imagine a healthy baby born premature 1 day early. Could you take a knife and stab it to death as it screams and cries? If not, perhaps it is indeed murder.