Unplanned pregnancies in the United States have declined by 18 percent over the past few years, a new Guttmacher Institute report found Wednesday.

In the report, the experts found that the rate of accidental pregnancies in American women between the ages of 15 and 44 fell from 54 out of 1,000 women in 2008 to 45 out of 1,000 in 2011. Declines were found in all groups regardless of factors such as age and income, but disparities still existed. For example, poor women were five times more likely to get pregnant accidentally than wealthier women.

"There were declines among women of all ages, incomes, and race and ethnicity groups. So the declines were seen across the board," said Mia Zolna, research associate at the Institute.

This step decline represents "the lowest level" that has been recorded in the past three decades, Zolna added. The researchers attributed the use of long-acting contraceptives as the reason behind the downward trend. Joerg Dreweke, the author of an accompanying article to the report, noted that from 2007 to 2012, the number of women who opted for intrauterine devices (IUDs) increased by more than three times.

Despite the drop in unintended pregnancies, the researchers found that the abortion rate for these cases remained very similar. From 2008 to 2011, the abortion rate increased slightly from 40 percent to 42 percent. The team noted that if lawmakers want to see abortion rates decline, they must increase access to birth control.

"These findings have major implications for the U.S. abortion debate as, among other things, they validate that supporting and expanding women's access to contraceptive services leads to a lower incidence of abortion," Dreweke wrote. "The clear implication for policymakers who wish to see fewer abortions occur is to focus on making contraceptive care more available by increasing funding and stopping attacks on all family planning providers."

Study author Lawrence B. Finer noted that since the data was collected before the Affordable Care Act was enforced, the rate of unintended pregnancies after 2011 has mostly likely continued declining.

The researchers had used a combination of data compiled by the U.S. National Survey of Family Growth and by the Institute's own surveys.

The report was published in the New England Journal of Medicine.