Legally, a human is human when there is brain function. You cannot legally pull the plug on an adult when there is brain function. There is no significant difference between the brain function of a human one minute before delivery as opposed to one minute after delivery.But that's just it. There isn't any "magic". It's a process. There is no magic moment (unless you're thinking of Ben E. King and The Drifters).
That said, the first breath starts the closing of a valve in the heart and the direction of blood flow is altered. That results in certain veins no longer being used, atrophying, then becoming cords/anchors to hold organs in place.
Consider, for a moment, if a human being's blood flow changed direction and veins atrophied. The word "calamity" would be appropriate. Furthermore, consider if the environment changed from the current gaseous one to a liquid as when a fetus goes from a liquid environment to a gaseous one. Completely submerge yourself in water and see how you function. Or take a fish out of water and observe how it functions.
Obviously, you are unaware of the changes from fetus to baby. Yours is a case of "a little knowledge is a dangerous thing."
Do some research. Understand the fundamental changes. While not magic moments they do occur relatively quickly.
It is pretensive and self-delusional to attempt to describe some difference that makes them magically inhuman before as to after such an event, and I suspect it is a willingness to justify the death of what one knows to be human. Just as the zygote is clearly genetically a separate human life from the mother, it is silly to attempt to say it is inhuman because it is early in development.
The question the sane argue is whether or not it is justifiably "human" in function. Can it think? Does it have a soul? That sort of thing. We have an understanding of what happens in the womb that we didn't when previous decisions on this topic were made. I surmise that changes will be apparent when next this topic is decided by the courts. I don't think the anti-abortion crowds will be satisfied, but I fully believe that only imminent danger of losing their life will allow any sort of abortion past the weeks when higher brain function begins. It is inconceivable that they would apply brain function at one point of a life cycle, but not at another.