There are merely gradations of development. That point is conceded by the more sophisticated philosophers arguing for choice on the abortion issue. You will find a lot of people who aren't sophisticated who use this and quite a lot of other bad arguments. What they have tried to do is make a distinction between humanness and personhood but you run into the same problem. Because it's a human from conception.
Human beings are personal type beings.
Personhood is a quality that inheres the very nature of a human. It is not a property that is developed later on. A human is a personal kind of being. There are other personal beings, by the way. Angels, for example.