I would also add that the law already recognizes unborn children as persons in some circumstances: if I leave my estate to my as-yet-unborn child, that unborn child has legal standing as a person in a probate proceeding.
The common law background on all this is ambiguous, because before the twentieth century society's attitudes were generally quite normal.
The concept of a woman intentionally murdering her own child - as opposed to an angry man killing a woman who bore his illegitmate child in order to avoid future claims on his property - was fairly alien.
Only unmarried women of high social rank had much to fear from illegitimate pregnancy. Married women of high social rank generally bore their illegitimate offspring and passed them off as legitimate. Women of lower social rank, married or unmarried, bore their illegitimate children and passed them off as relatives' children or left them as foundlings.
It wasn't until the twentieth century - when there emerged a large urban upwardly-aspiring middle class of leisured women as well as surgically less-risky abortion - that abortion became popular.
The common law was not formulated in an age when there were millions of unmarried women in their twenties who thought that motherhood was an avoidable inconvenience.
Good. I would point out that the Fourteenth Amendment explicitly guarantees the right to life of every person.However, it only protects people from state action, not private action. Only state penal codes protect people from private action.