What did the researchers find? Well, it’s definitely not about sex. The report found that for every income bracket, just about two-thirds of women had sex in the past year. In fact, women in the highest income bracket reported the highest rate of activity, with 71 percent saying they'd been sexually active. That means that the actual level of sexual activity has little to do with why poorer women are more likely to unintentionally get pregnant and bear children.

It’s also not really about the lack of motivation to prevent pregnancy. “I do think there's something to the idea that there's a bit of a trade off, that the more you have to lose the more determined you are likely to be to use contraception and perhaps access abortion,” says Richard Reeves, one of the study’s co-authors and a senior fellow in economic studies at Brookings. “The danger of that idea is that it might make one a bit complacent about the sort of gaps we find. I think that the evidence is much more strongly on the other side of the equation, that it's access to effective and safe forms of contraception and abortion.”

When it comes to the notion that poorer women may be less worried about getting pregnant than their more affluent counterparts (leading them to be more lax in contraception use)—the answer isn’t cut and dry. Across all income groups, the study asked women who were not trying to conceive whether they’d be upset if they did get pregnant. And for each income level the results were pretty much the same, with about one in three women saying they would not be all that upset if they got pregnant, while two-thirds considered such a possibility very upsetting. According to Reeves, intent to get pregnant—or the level of motivation not to—is particularly hard to assess. “You will find some people who are saying, ‘I never want to get pregnant, but I'm not using contraception,’” he says.

Response to Question: How Would You Feel If You Got Pregnant

Brookings Institution

Unsurprisingly, the gaps in contraception use were significant between the most and least affluent. Among the wealthiest women, only 11 percent of those who had sex reported not using contraception, for those in the poorest group the rate was more than twice as high. Naturally, that led to a higher rate of pregnancy for lower-income women: 9 percent versus only 2.9 percent for those who had the highest incomes.

The study notes that while contraception coverage is a requirement for many federally-backed insurance plans, abortion (except in the case of rape, incest, or life-threatening emergency) is prohibited by programs that utilize federal funding, like Medicaid—leaving low-income recipients to pay for the procedure with their own money.