Last week, the Guttmacher Institute, a pro-choice think tank based in New York, released a study showing that the abortion rate in the United States has fallen to its lowest level since 1973, when Roe v. Wade became the law of the land. Based on a comprehensive survey of abortion providers in all fifty states, the study found that the number of pregnancy terminations performed between 2008 and 2011 decreased by thirteen per cent. The decline was generally hailed as welcome news by advocates on both sides of the abortion conflict. “The right-to-life movement is succeeding,” Carol Tobias, the president of the National Right to Life organization, said of the findings. Cecile Richards, the president of Planned Parenthood, responded by tweeting, “PP is proud to provide abortion & #BirthControl that prevents the need for abortion in the first place.”

Less widely noted was another, more disquieting trend: the increasingly pronounced class and racial divisions within the population of women having unintended pregnancies and abortions. As I noted in an article in the magazine on a troubled chain of clinics, the over-all abortion rate fell by eight per cent between 2000 and 2008 but rose among poor women by eighteen per cent. Last December, another Guttmacher Institute study revealed that, during this same eight-year period, the rate of unintended pregnancies was more than five times higher among poor women than among women whose income was at least twice the federal poverty level. The same report found that significant ethnic and racial differences existed even when controlling for income, with the rate of unintended pregnancies among minority women more than twice the rate among white women.

It is possible that these disparities have narrowed slightly in recent years (the data collected by the Guttmacher Institute in its most recent study has not yet been sorted by income and race). But few analysts are betting on this. “I think we will very likely see a continuing disparity between wealthier women and non-wealthy women—the poor and the non-poor—as well as a disproportionate representation of women of color,” says Carole Joffe, a sociologist at the University of California, San Francisco, and the author of several books about abortion.

Low-income women tend to have less access to the most reliable forms of birth control—in particular, long-acting intrauterine devices (I.U.D.s), which are extremely effective, and which the new Guttmacher study touted as a potential factor behind the recent decline in the over-all abortion rate. It was not the first study to suggest such a link. In 2012, an article published in the journal Obstetrics and Gynecology reported on an experimental project in St. Louis, where between 2007 and 2011 a cohort of nine thousand two hundred and fifty-six adolescents and women at high risk for unintended pregnancies were informed of the superior effectiveness of I.U.D.s and offered the contraceptive method of their choice at no cost. The abortion rate in this group promptly fell to less than half of the regional and national rates.

Thanks to publicly funded family-planning services provided to poor women under Title X—a federal program that House Republicans have repeatedly tried to eliminate—there is evidence that more low-income women have been using I.U.D.s in the past decade. But the total number of users is still small, and the cost, which can exceed a thousand dollars before insertion, remains prohibitive for many low-income women who don’t qualify for Medicaid and cannot afford private insurance. “We know that cost is a major factor in a woman’s ability to choose and access a method of contraception that works best for her, and behind the cost is access to health-insurance coverage,” Kinsey Hasstedt, a public-policy associate at the Guttmacher Institute, told me.

While the Affordable Care Act could potentially expand coverage and force companies to provide contraceptive services to all of their workers, low-income women in states that opted out of the Medicaid expansion won’t benefit. The same is true for women working for religious institutions that claim an exemption. Some for-profit companies have also challenged the contraception mandate for employees on religious grounds, a matter to be argued before the Supreme Court in March.

To be sure, not all women who have unintended pregnancies wind up visiting abortion clinics nowadays, but the reason is not necessarily that they have come to believe that “killing unborn children is wrong”—the explanation that Carol Tobias, of National Right to Life, offered for why the abortion rate has fallen. An alternative explanation is that more and more women live in places where there are no clinics within driving distance, a particularly grave problem for those who don’t have much money. In a recent article in The New Republic, Lindsay Beyerstein described the situation in the Rio Grande Valley, in Texas, where women who cannot afford the five-hundred-mile trip to a clinic in San Antonio increasingly slip across the border with Mexico to buy misoprostol, an ulcer medication that can induce miscarriages but can also cause bleeding and other adverse effects. Lester Minto, a physician who used to work at a clinic in the Valley but had to stop because he lacked local hospital-admitting privileges—a requirement for all providers under Texas’s strict new abortion law—told Beyerstein that he had seen two hundred women suffering complications from self-induced abortions since the restrictions went into effect. These women shared one common trait: they were poor.

The latest Guttmacher study did not measure how new regulations enacted in states like Texas may alter the demand for abortion, not least since most of these laws were enacted only after 2011. If what’s happening in the Rio Grande Valley is any indication, the official abortion rate will likely fall further in the years to come, but not for reasons that will be welcome news to supporters of reproductive rights. And women of lesser means will almost surely feel the negative repercussions most.

Read Margaret Talbot on the Guttmacher Institute’s new study.

Photograph by fotofrog/Getty.