Poor women are five times as likely as affluent women to have an unintended birth, and the reason boils down to access to the most reliable birth control, a new paper from the Brookings Institution concludes.

The study, which used data from a government survey of family growth, examined fertility outcomes of 3,885 single women, none of whom were trying to get pregnant. Those living below the poverty line were twice as likely to have unprotected sex as those with incomes four times the poverty line.

Previous research suggests poor women "control their fertility less carefully because they have less to lose," the authors noted. But the new study surveyed women across income levels about their attitudes on unexpected pregnancies and found no difference.

Though the Affordable Care Act has improved financial access to contraception, "lack of knowledge" and lack of medical advice about long-acting, highly reliable methods such as IUDs and implants "are still significant problems," the authors wrote.

Wealthier women who faced unplanned pregnancies were also far more likely to have abortions.

- The Washington Post