I understand what you mean about the difficulty of fixing a point and saying 'on this day abortion is fine, but one day longer and it is murder'.
However that point does have to be fixed somewhere, even accepting that it will be by definition partly arbitarty.
The point where you make the distiction is to far advanced for me. Saying that the birth must be fully completed means that it is acceptable to kill the baby if even one toe is still inside its Mother, while it would be murder the second the toe slips out.
I can't believe that in reality this is something you would be happy with. Yes, drawing any line will be blurred and require moral compromise, but i am certain that that line should be drawn further back than the moment of birth.