A dramatic new study with implications for next month’s presidential election finds that offering women free birth control can reduce unplanned pregnancies—and send the abortion rate spiraling downward.

When more than 9,000 women ages 14 to 45 in the St. Louis area were given no-cost contraception for three years, abortion rates dropped from two-thirds to three-quarters lower than the national rate, according to a new report by Washington University School of Medicine in St. Louis researchers.

From 2008 to 2010, annual abortion rates among participants in the Contraceptive Choice Project - dubbed CHOICE - ranged from 4.4 abortions per 1,000 women to 7.5 abortions per 1,000. That’s far less than the 19.6 abortions per 1,000 women nationwide reported in 2008, the latest year for which figures are available.

Among teen girls ages 15 to 19 who participated in the study, the annual birth rate was 6.3 per 1,000 girls, far below the U.S. rate of 34.3 per 1,000 for girls the same age.

The study’s lead author, Dr. Jeffrey Peipert, a professor of obstetrics and gynecology at Washington University, expected both measures to fall, but even he said he was “very surprised” by the magnitude.

In all, Peipert said, one abortion was prevented for approximately every 100 women who took part (the actual estimate is 1 per every 79 to 135 women).

The results were so dramatic, in fact, that Peipert pushed the journal of Obstetrics & Gynecology to publish the study before the Nov. 6 presidential election, knowing that the Affordable Care Act, and its reproductive health provisions, are major issues in the campaign.

“It just has so many implications for our society,” he told NBC News.

Several factors contributed to the declines, he argued. First, a large majority of the women in the study were encouraged—and chose—to use intrauterine devices, or IUDs, and hormonal implants over more commonly used birth control pills.

Because birth control pills require strict adherence, and people forget to take them, that method fails about 8 percent of the time. IUDs and implants are over 99 percent effective.

Second, program enrollees included high-risk populations like women and girls who’ve already used abortion services once—and are more likely to have a second abortion—and women and girls who are economically distressed and may not have means to obtain contraceptive products and services.

That’s important because an IUD, including the device and the physician’s service to place it in the uterus, can cost between $800 and $1,000. Since an IUD lasts at least five years, it saves money in the long run over a monthly cost of roughly $15-$25 for pills, but the up-front charge is prohibitive for many women.

James Trussell, a Princeton University professor of economics and public affairs and an expert in family planning called the results “terrific, great work, and a very important demonstration project.”

But it’s also politically fraught. The Affordable Care Act requires insurance plans to cover contraceptive costs. That’s led to conflicts among the Obama administration, the Catholic church, and the church’s political allies who argue that requiring a Catholic employer to provide such insurance contradicts the church’s teaching and represents a breach of religious freedom.

Conservatives have also objected to contraceptive coverage on cost grounds. Some have focused their anger at Sandra Fluke, a Georgetown University law student who agitated for the Catholic school to offer an insurance plan that covers contraception. Radio host Rush Limbaugh famously called her a “slut” and a “prostitute.”

But experts, including Peipert, point out that no-cost contraception saves money.

According to a 2011 study from the Guttmacher Institute, unplanned pregnancies costs the United States a conservatively estimated $11 billion per year.

“The way I look at it as a gynecologist with an interest in women’s health and public health and family planning, is that this saves money,” Peipert said. “When you provide no-cost contraception, and you remove that barrier, you finally reduce unintended pregnancy rates. It doesn’t matter what side one is on politically, that’s a good thing.”

The Catholic Church is unlikely to be moved. “If, as supporters of the contraceptive mandate argue, it will pay for itself in reduced medical expenses, so will free embryo engineering and other eugenic services, including infanticide, doctor-assisted suicide, organ harvesting, and genetic manipulation,” wrote Thomas Joseph White, director of the Thomistic Institute at the Dominican House of Studies in Washington, D.C., and R.R. Reno, in the conservative journal First Things.

But to academic experts, the results of CHOICE are clear. “What the study suggests to me,” said John Santelli, professor at Columbia University’s Mailman School of Public Health, “is that it’s totally supportive of the president’s provisions on reproductive care and preventive services for women in the Affordable Care Act.”

In a 2009 study, Trussell and colleagues reported that long-acting contraceptives like IUDs were far cheaper than an unintended birth, an abortion, and especially an ectopic pregnancy.

Trussell argued that cost savings go “well beyond” those immediate medical savings. They don’t, for example, take into account costs associated with longer term issues such as economic stress on the mother and family, a teenager who doesn’t finish high school or skips college because she’s had a baby.

Research has also shown that neglect, stress, anxiety, or simply a low level of nurturing in early life has effects on a child that can last far into adulthood. It may influence, for example, the cycle of teen pregnancy and crime.

“It’s hard to imagine how politicians wouldn’t like to spend a dollar to save four,” Trussell said. As to the objections like those of White, he concluded that “it makes no sense whatsoever. Regardless of your views on abortion, virtually everybody says preventing unintended pregnancies is smart.”

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By Brian Alexander, NBC News Contributor
Brian Alexander is co-author, with Larry Young Ph.D., of “The Chemistry Between Us: Love, Sex and the Science of Attraction,”  now on sale.