A new analysis of global abortions shows a stark and troubling divide between what's happening in wealthier, developed countries and their poorer and less developed counterparts.

The paper, published Wednesday in the Lancet journal, represents the most comprehensive analysis ever conducted on the subject. It shows an average of 56 million abortions took place annually worldwide from 2010 to 2014. That translates to 35 procedures per every 1,000 women of childbearing age, meaning that roughly 3.5 percent of women in this age group had an abortion.

The numbers are significantly smaller than a decade earlier -- from 1990 to 1994, there were on average 40 abortions annually per every 1,000 women -- and should be a cause for celebration for many in the reproductive-health field and for those who oppose abortion. But Gilda Sedgh, a principal research scientist with the Guttmacher Institute in New York and lead author of the study, cautioned in a call with reporters that "the global picture masks differences between the developed and developing world."

No matter how you crunch the numbers about the developed world, which includes the United States, abortion rates are falling. Rates have been declining for 25 years and are now at a historic low. There were 27 abortions per 1,000 women in 2010 to 2014, down from 40 per 1,000 in 1990 to 1994. Likewise, the total number of abortions fell from 12 million to 7 million.

But in developing countries during the same period, abortions went from 39 to 37 per 1,000 women while the total number of procedures spiked from 39 million to 50 million annually -- a situation that the authors blame on lack of access to modern methods of contraception that could have reduced unwanted pregnancies.

"We think this is because the desire for small families and precisely timed births has outpaced the uptake of contraceptive use," Sedgh said.

The study was based on statistical modeling of information collected from national surveys, official government statistics, and other published and unpublished studies, and it was funded by various countries as well as the David and Lucile Packard Foundation and the United Nations.

Among the other major findings are that three-fourths of abortions took place among married women, challenging the popular notion that most abortions are sought by unwed teens.

Eastern Europe was the standout with the biggest drop in abortion rates, from 88 to 42 per 1,000 women. Rates also fell in Southern Europe, from 38 to 26; in Northern Europe, from 22 to 18; and in North America, from 25 to 17.

Researchers said western Europe was the only studied region with an increase in its abortion rate, which they said might have been because of a growing foreign-born population.

Beyond providing a breakdown on abortion around the world by major region, the study also touched on the sensitive legal and ethical debates about the procedure by breaking out numbers for the 58 countries where it is illegal or permitted only to save a woman's life. The authors noted that the rate in those countries -- representing most of South America, Africa and the Middle East -- is 37 per 1,000. That's "essentially" no different from the 34 per 1,000 rate in the 63 countries where abortion is legal.

The authors emphasized that these findings suggest that "restrictive abortion laws do not limit the number of abortions."

In a commentary piece also published by the Lancet, associate professor Diana Greene Foster of the University of California at San Francisco was critical of this reasoning.

"The obvious interpretation is that criminalizing abortion does not prevent it but, rather, drives women to seek illegal services or methods. But this simple story overlooks the many women who, in the absence of safe legal services, carry unwanted pregnancies to term," Greene Foster said. She argued that it does not make sense to assume "a one-for-one exchange of illegal abortion for legal abortion."

The paper's findings are consistent with other data released in recent years that show a positive trend in the reduction in unwanted pregnancies and births. This month, the U.S. Centers for Disease Control and Prevention reported that the birthrate among American teenagers -- which was at crisis levels in the 1990s -- had fallen to an all-time low and that the decline affected all regions and all races.

While various cultural, educational and economic factors have been debated as reasons why some groups have higher rates of abortion than others, many physicians, researchers, women's right advocates and public health officials appear to now agree on a core factor: access to modern methods of birth control.

The past 10 years have been breakthrough ones for contraceptive innovations; women can now avail themselves of all kinds of  long-lasting, low-risk implantable and injectable alternatives to the daily pill. Yet much of this information and the availability of the new methods haven't filtered down to developing parts of the world.

"Clearly, efforts have to focus on these regions," said Bela Ganatra of the World Health Organization, who co-authored the study. She added that health officials recognize that not all unsafe abortions can be prevented by increasing access to contraception because some women are seeking the procedure due to rape or the failure of contraceptives or other factors. Another study is underway to try to ascertain more information about the situations that result in a safe or unsafe abortion, she said.

Read more:

Like our Health & Wellness page on Facebook for more science news about the ins and outs of the human body and mind, essays and advice. You can sign up here for our newsletter.