Scientific progress is remaking the debate around abortion. When the U.S. Supreme Court decided Roe v. Wade, the case that led the way to legal abortion, it pegged most fetuses’ chance of viable life outside the womb at 28 weeks; after that point, it ruled, states could reasonably restrict women’s access to the procedure. Now, with new medical techniques, doctors are debating whether that threshold should be closer to 22 weeks. And that’s just for starters.