On Friday, the legislature of Missouri passed a ban on abortions, among the most extreme of any state. It prohibits any abortions after eight weeks of gestation, putting it among the category of misleadingly named “heartbeat bills” that use fetal cardiac activity as a marker for … well, illegality, really. Like a law signed earlier last week in Alabama, the Missouri bill contains no exceptions for cases of rape or incest. That makes eight US states with similar extreme bans on their books—each vying to be the law that makes its way to the Supreme Court and overturns Roe v. Wade, the 1973 decision that made abortion legal in the United States.

None of the restrictions have gone into effect, either because of delays built into the legislation itself or legal challenges. If they do, they’ll spark an unintentional, vast experiment in public health. Already, states with the most restrictions on access to abortions are also those with the highest rates of maternal and infant mortality. The connection isn’t direct—abortion access can be a kind of proxy for access to all sorts of pre- and postnatal health care, not to mention correlating roughly with better-funded education systems, lower poverty rates, and tighter environmental regulation. But evidence from history does suggest a hypothesis: More women and babies are going to get sick, be poor, and die.

In the mid 2000s, billboards worrying about the mental health of women who’d gotten abortions were common, and justices on the Supreme Court expressed concern that those women might experience psychologically damaging “regret.” Diana Greene Foster, a demographer and director of research at the Advancing New Standards in Reproductive Health program at UC San Francisco, started wondering if any of that was true. Until then, most research looking at abortion outcomes compared women who’d gotten one to women who’d gotten pregnant and had a baby. That’s science—isolate the thing you want to study by looking at people who have it and people who don’t.

It’s not great science, though, because, as Foster realized, the control group wasn’t actually controlling. It didn’t isolate the variable. What you really need to do is to look at women with unwanted pregnancies who sought an abortion, and compare those who got one with those who did not. “If you make abortion restrictions, who they’ll affect are people who want abortions and get births, so it was important to get the science right,” Foster says. “What’s the effect if women are able to get the abortion they want? Or can’t get the abortion they want?”