Some adults were regarded as less than human. I honestly don't know about native Americans. Were they regarded as citizens, being born here? Enquiring minds want to know.
You know very well they were not so regarded at the time. What does that have to do with the status of unborn children?
Incidentally, I read somewhere recently that in my home state (Massachusetts), back in the late colonial period attempts were made to enslave the native Indians. But the attempt had to be given up: The Native Americans were just too "shiftless" and undependable, and had the bad habit of always successfully escaping. If you could manage to recapture them, they'd just run away again at the first opportunity. IOW: You really couldn't enslave the native Americans. They simply refused to play along.
Native Americans were counted as citizens of a hostile nation, or as citizens of a conquered nation. Nowadays they are U.S. citizens and also tribe-members. Not up on tribal law so I don’t know all the specifics.
And although I am against abortion, I think the Constitution says you have to be born to have rights. The Constitution mentions being born twice. Until you are born you have no rights and are dependent upon the resources of an American citizen in order to attain viability, and that citizen has been found to have the right (through emanations and penumbras)to deal with that issue involving a non citizen of the U.S.A.. I find it hard to disagree with a decision of the U.S. Supreme Court that finds any right left for us in the shambles this government has made of the Constitution, despite the penumbras; especially when it deals with the rights of U.S. citizens over those who are not.