The existence of "personhood" was but one of the issues discussed by the Supreme Court in Roe v. Wade. More central in its discussions and ultimate determination was the issue of "potential life".
From the majority opinion by Justice Harry Blackmun:
"In view of all this, we do not agree that, by adopting one theory of life, Texas may override the rights of the pregnant woman that are at stake. We repeat, however, that the State does have an important and legitimate interest in preserving and protecting the health of the pregnant woman . . . and that it has still another important and legitimate interest in protecting the potentiality of human life. These interests are separate and distinct. Each grows in substantiality as the woman approaches term and, at a point during pregnancy, each becomes "compelling."
In all of the opinions written by the Justices, the issue of "potential life" is that most argued.
"Get it right", indeed.