Abortion was legal under the Anglo Saxon common law which was entrenched into the Constitution in the 4th Amendment: Amendment 7 - Rights in Civil Cases In suits at common law, where the value in controversy shall exceed twenty dollars, the right of trial by jury shall be preserved, and no fact tried by a jury shall be otherwise reexamined in any court of the United States than according to the rules of the common law.
This is what is usual The argument is dragged around to late term abortions even though they are a very very small percentage and usually performed for catastrophic circumstances