Scott Klusendorf says that there are only four differences between a pre-born and newborn. He uses the acronym S.L.E.D.
Size: Does how big you are determine who you are?
Level of development: Are 20-year-olds more human than 14-year-olds, since they are smarter and stronger?
Environment: Does being inside a house make you more or less of a person than being outside? Does being located in his mother’s body rather than outside make a child less human?
Degree of dependency: Does dependence upon another determine who you are? Is someone with Alzheimer’s or on kidney dialysis less of a person?
The question is not how old or big or smart or inconvenient the unborn are, but who they are. The answer is simple: they are human beings. (“Why Pro life?” Randy Alcorn, Pg. 31)