The app, Natural Cycles, calculates when a woman is most likely to be fertile using their daily body temperature data and their menstrual cycle information.
The app then tells users what days they are more likely to be fertile and should abstain from sex or use protection if they do not wish to get pregnant.
"Consumers are increasingly using digital health technologies to inform their everyday health decisions, and this new app can provide an effective method of contraception if it’s used carefully and correctly," Dr. Terri Cornelison, the assistant director for the health of women in the FDA’s Center for Devices and Radiological Health, said in a statement.
"But women should know that no form of contraception works perfectly, so an unplanned pregnancy could still result from correct usage of this device," she added.
The app had a "perfect use" failure rate of 1.8 percent in clinical studies that involved more than 15,500 women, or a "typical use" failure rate of 6.5 percent, according to the FDA. The "typical use" failure rate took into account women who sometimes did not use the app correctly or may have had unprotected sex on a day when the app flagged that they were fertile.
Natural Cycles has, however, courted controversy in Europe, as some women have reported unwanted pregnancies while using the app as their main form of birth control.
Sweden's public broadcasting company SVT reported that 37 out of 668 women who received an abortion at a Stockholm hospital from September 2017 to the end of December 2017 were using the app and still had an unwanted pregnancy.
ABC News' chief medical correspondent Dr. Jennifer Ashton emphasized that no method of contraception is perfect except abstinence, so it's not completely surprising that women have still gotten pregnant while using it.
Ashton added that apps can be useful in that they enourage women to be aware of their bodies' monthly changes. If a woman does decide to use an app for birth control, however, she needs to have a plan for what she would do if she does have an unplanned pregnancy.
Most contraception pills have a "typical use" failure rate of approximately 9 percent, according to Ashton, which is actually higher than the rate of the app, the FDA's data showed.
Still, Asthon says that women should ask their doctors about risks, benefits and alternatives for any contraceptive method they are using.