A health worker teaches women how to properly use a intra uterine device (IUD) during the World Population Day in Manila. (Jay Directo, AFP/Getty Images)

NEW YORK (Reuters Health) - During a four-year experiment that offered the women of St. Louis, Missouri, free contraceptives - including expensive long-term implants - rates of teen pregnancy and repeat abortions in the area dropped dramatically, according to a new study.

Researchers say the project, begun in 2007, was intended to model the likely benefits of mandatory insurance coverage for contraception under the Affordable Care Act.

"We believe that this is a major step to reducing unintended pregnancy in the United States," said lead author Dr. Jeffrey Peipert, a professor at Washington University School of Medicine in St. Louis.

Peipert and his colleagues write in the journal Obstetrics & Gynecology that unintended pregnancies lead to one million births each year, at a cost to tax payers of $11 billion.

According to the Centers for Disease Control and Prevention, there were 825,000 abortions in the U.S. in 2008, the latest year for which figures are available.

Birth control can prevent unwanted pregnancies, but a number of obstacles often face women who want to use contraception - particularly the long-term but reversible kind such as intrauterine devices (IUDs) and hormonal implants inserted under the skin of the arm.

Both methods can prevent pregnancy for years and are considered to be the most effective forms of birth control.

But they come with a large upfront price tag, around $700, said Peipert, which prevents some women from choosing a long-acting birth control.

Doctors and nurses can also present obstacles, he added.

"Many doctors and nurse practitioners are reluctant to use IUDs in women who are at risk for infection. They also fear it can cause infertility. Many of these are myths we need to get past," Peipert told Reuters Health.

To address such barriers to access, and to promote long-acting contraceptive methods, Peipert and his colleagues set up the Contraceptive CHOICE Project, with funding from the Susan Thompson Buffett Foundation, in St. Louis.

Between 2007 and 2011, a total of 9,256 women enrolled and were offered any FDA-approved contraceptive they wanted after counseling about the various choices, their effectiveness, risks and benefits.

The researchers also educated doctors and nurses in the program about long-acting birth control, and urged them to encourage women to opt for these methods.

Among the women who participated in the project, 63 percent had previously had an unintended pregnancy and 41 percent had had an abortion.

Most women - 75 percent - chose a long-acting method of contraception.

Overall, abortions, repeat abortions and teen pregnancies all dropped in St. Louis while rates elsewhere in Missouri remained stable, Peipert's team found.

From 2008 to 2010, for instance, the number of abortions in the St. Louis metropolitan area declined by 20 percent, while the rate of abortions in the rest of Missouri remained unchanged.

Similarly, in St. Louis the proportion of abortions requested by women who had had one previously fell from 47 percent in 2006 to 39 percent in 2010.

In comparison, repeat abortions in Kansas City, Missouri, rose from 46 percent to 51 percent during the same time period.