I could see the similarities, as Slavery was more objectifying humans as property , and the argue for Abortion is sometimes said that they aren't human at all yet, and just a pile of goo that has a Heart beat. It's in the womans body so that gives her the "ownership" of it and then giving her the option of abortion. Maybe?
I agree that both aren't acceptable, But also some will argue that Abortion is an option if the baby most likely will not survive the birth and the mother will not if the baby is not aborted. I think that is too much of a personal decision to say a straight yes or no.