Related: Mobile app designed to prevent pregnancy approved in Europe
More than 15,570 women used the app for a clinical study over the course of eight months. The “perfect use” failure rate was 1.8 percent, meaning 1.8 in 100 women who use the app for a year will get pregnant because their contraceptive method failed when they had intercourse on a fertile day, or they had intercourse when the app predicted they would not be fertile.
Related: Hospital blames contraceptive app for accidental pregnancies
The “typical use” failure rate was 6.5 percent, meaning women used the app incorrectly. For example, a woman may have unprotected sex on a day the app predicted they would be fertile.
In January, a Swedish Hospital blamed the app for reports of dozens of unwanted pregnancies from users, but officials with the company that marketed it noted that "unwanted pregnancies is an unfortunate risk with any contraception."