Earlier this year, the Affordable Care Act began requiring private insurance agencies to offer many contraceptives at no cost to consumers. This change was an effort to remove cost as an obstacle to women to choose to use birth control. It might also have the added benefit of reducing abortion rates, according to new research published online October 4 in Obstetrics & Gynecology.

The study found that the availability to free contraception caused a drop in teen birth rates and cut the rate of abortions for all participants by more than half. "The impact of providing no-cost birth control was far greater than we expected," Jeff Peipert, a professor of obstetrics and gynecology at Washington University in St. Louis, and study co-author, said in a statement.

For the study, Peipert and his colleagues recruited 9,256 women and adolescent girls, aged 14 to 45, in the St. Louis area who were at particular risk for unintended pregnancies and who wanted to avoid pregnancy for at least a year. Those who opted to participate in the three-year study had the choice of either shorter-acting methods, such as pills, vaginal rings or patches or long-acting reversible methods, such as intrauterine devices (IUDs) or implants. The IUDs consist of a small T-shaped device that is inserted into the uterus, and the implant is a thin plastic strip that is inserted under the skin of the upper arm; both require insertion in the doctor's office. Study participants received their chosen method (with the option to change methods) at no cost. After learning about the risks and benefits of all types, 75 percent of the women chose the longer-acting IUDs and implants (particularly because of their low failure rate and not having to rely on regular adherence and need to seek replacements).

Abortion rates among study participants were below 7.6 per 1,000—less than half of the national rate of 19.6 per 1,000—even though the study participants were considered to be at higher risk than the general population. These rates suggest that the same free birth control options available nation wide would prevent one abortion for every 137 or fewer women and teens who participated, say the researchers. Teens in the study had babies (the majority of which come from unintended pregnancies) at a rate lower than one fifth of the national average: 6.3 per 1,000 in the study and 34.3 per 1,000 in the U.S.

The study followed the Institute of Medicine's recommendations that all U.S. Food and Drug Administration-approved contraceptive methods be available to women without cost under the 2010 Affordable Care Act. The group's report also noted that women should receive "a fuller range of contraceptive education, counseling, methods and services so that women can better avoid unwanted pregnancies and space their pregnancies to promote optimal birth outcomes." The researchers estimate that if a similar program were rolled out nationwide, more than 40 percent of the more-than 1 million abortions received annually (pdf) would be avoided (a slightly smaller drop because the study participants were a high-risk subgroup of the population).

"We think improving access to birth control, particularly IUDs and implants, coupled with education on the most effective methods has the potential to significantly decrease the number of unintended pregnancies and abortions in this country," Peipert said.

Although birth-control subsidies involve upfront costs, in the long run they offer savings—every 1 million unintended births cost taxpayers $11 billion each year, according to a 2011 study in Contraception. The rate of unintended pregnancies in the U.S.—49 percent, according to the U.S. Centers for Disease Control and Prevention (CDC)—far exceeds that of most developed countries. Most women in the U.S. rely on birth control pills for contraception, which is less expensive upfront but less reliable than IUDs and implants, which require an outlay of at least $800 but remain effective for three or more years.