The U.S. abortion rate has fallen by 25 percent in recent years, according to a report published in the American Journal of Public Health on Thursday.

However, the procedure remains common. One in four women will have an abortion by 45.

Researchers used data from three surveys, two conducted by the federal government and the third by the Guttmacher Institute, to estimate abortion rates.

Why the decline?

Co-authors Rachel K. Jones and Jenna Jerman, who work for the research division of Guttmacher, suggested that the main factor driving the decline in abortions was improvements in contraceptive use.

Definitive data on unintended pregnancies for that period isn’t available yet, but there are other indicators that support this theory:

The biggest decline in abortions was 46 percent among women ages 15 to 19. There has been strong evidence that contraceptive use, such as more reliance on long-acting methods and intrauterine devices, was responsible for that decrease. Jones and Jerman also noted that for the first time in 20 years, failure rates for condoms improved.

Health care and income

The abortion rate was the highest among women with incomes less than 100 percent of the federal poverty level — or about $19,790 for a family of three.

Abortions seem to be increasingly concentrated among the poor. However, this is the first time in 20 years that the abortion rate has declined in this group. Researchers said that we might have expected to see an even greater decline given new state restrictions on abortions.

Between 2008 and 2014, numerous states — including Indiana, Kansas, Texas and North Carolina — enacted new restrictions, waiting periods or mandatory ultrasounds for women considering abortions in those states.

But in other parts of the country, the Affordable Care Act’s Medicaid expansion helped women who might not otherwise have been able to get an abortion get insurance coverage for one.

“It’s possible more poor women in states where Medicaid pays for abortion acquired coverage and were able to use it to pay for their procedure,” researchers said.

The divergence in abortion trends by income in the United States is similar to the divide that exists in the rest of the world. A recent study in the journal Lancet found that in wealthier countries, abortion rates are falling, while abortion rates are rising in developing countries, a situation that the authors say may be due to a lack of access to modern methods of contraception among the poor, leading to more unwanted pregnancies.

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