A new study has found that long-acting forms of birth control may work one year longer than their approved duration of use, and researchers are studying whether they may be effective another two years beyond that.

“This research is important because extended use of these devices will reduce cost to both the individual and insurer and improve convenience for women, who can delay removal and re-insertion,” study author Colleen McNicholas, assistant professor of obstetrics and gynecology at Washington University, said in a news release.

The study authors, who published their findings online Thursday in the journalObstetrics & Gynecology, examined 237 women who used contraceptive implants and 263 women who used hormonal intrauterine devices (IUDs).

Contraceptive implants are matchstick-sized rods that are inserted into the arm and are approved by the Food and Drug Administration (FDA) for three years. IUDs are T-shaped devices fitted inside the uterus that prevent the implantation of fertilized ova and, depending on the brand, are FDA-approved for anywhere from three to 10 years. The researchers studied the IUD device Mirena, which is effective for up to five years, and the implants Implanon and Nexplanon.

According to the news release, the women in the study were 18 to 45 years old, and their contraceptives had to be within six months of expiring when they enrolled. Researchers notified the study participants of a risk for becoming pregnant if the devices were used past their confirmed duration of efficacy.

One year after having unprotected sex with use of the long-lasting contraceptives, none of the women with the implant got pregnant, while one woman who used an IUD got pregnant. Study authors said that failure rate was similar to that of IUDs used within the recommended five-year time frame, according to the news release.

In their ongoing study, researchers plan to enroll a total of 800 women, including the participants from the current portion of the study, to determine whether the contraceptives could last up to three years.

While a recent analysis suggests long-acting forms of birth control are less popular than condoms and birth control pills, which are the second and first most-used types of contraception, data show that the use of IUDs and implants is on the rise. According to a Guttmacher Institute analysis of data from the federal National Survey of Family Growth, about 12 percent of women who used contraceptives between 2011 and 2013 used IUDs or hormonal implants, up from only 2.4 percent in 2002.

“The longer a contraceptive method is effective, the bigger the impact it can have,” senior author Jeffrey Peipert, professor of obstetrics and gynecology at Washington University said in the news release. “In the long term, this work has the potential to change how we provide contraceptive methods around the world and can enable women to control their reproductive health and family size.”