When Diana Greene Foster, a demographer and an associate professor of obstetrics and gynecology at the University of California, San Francisco, first began studying women who were turned away from abortion clinics, she was struck by how little data there were. A few clinics kept records, but no one had compiled them nationally. And there was no research on how these women fared over time. What, Foster wondered, were the consequences of having to carry an unwanted pregnancy to term? Did it take a higher psychological or economic toll than having an abortion? Or was the reverse true — did the new baby make up for any social or financial difficulties?

“It’s not that the study was so hard to do,” Foster says. But no one had done it before. Since Roe v. Wade was decided in 1973, the debate over abortion has focused primarily on the ramifications of having one. The abortion rights community maintains that abortion is safe, both physically and psychologically — a position most scientists endorse. Those on the anti-abortion side argue that abortion is immoral, can cause a fetus pain and leads to long-lasting negative physical and psychological effects in the women who have the procedure. There is no credible research to support a “post-abortion syndrome,” as a report published by the American Psychological Association in 2008 made clear. Yet the notion has influenced restrictive laws in many states. In Alabama, women who seek an abortion must have an ultrasound and be offered the option to view the image; in South Dakota, women must wait at least 72 hours after a consultation with a doctor before having the procedure. “The unstated assumption of most new abortion restrictions — mandatory ultrasound viewing, waiting periods, mandated state ‘information,’ ” Foster says, “is that women don’t know what they are doing when they try to terminate a pregnancy. Or they can’t make a decision they won’t regret.” Lost in the controversy, however, is the flip side of the question. What, Foster wondered, could the women who did not have the abortions they sought tell us about the women who did?

Most studies on the effects of abortion compare women who have abortions with those who choose to carry their pregnancies to term. It is like comparing people who are divorced with people who stay married, instead of people who get the divorce they want with the people who don’t. Foster saw this as a fundamental flaw. By choosing the right comparison groups — women who obtain abortions just before the gestational deadline versus women who miss that deadline and are turned away — Foster hoped to paint a more accurate picture. Do the physical, psychological and socioeconomic outcomes for these two groups of women differ? Which is safer for them, abortion or childbirth? Which causes more depression and anxiety? “I tried to measure all the ways in which I thought having a baby might make you worse off,” Foster says, “and the ways in which having a baby might make you better off, and the same with having an abortion.”

Foster began by gathering data locally. She ran the study out of her office at U.C.S.F. (I am a student in the U.C. Berkeley-U.C.S.F. Joint Medical Program but did not know Foster before reporting this article.) When the counselors at a nearby abortion clinic received a woman who was too far along to terminate her pregnancy, they called Foster, who would run over and arrange to interview the patient. Given the stigma attached to seeking an abortion later in pregnancy, Foster expected that many women would be reluctant to be part of her study. But four out of five women agreed to participate. “Sometimes, if you tell them that their experience is valuable, that it might help other people in their situation, they will come through,” she says.