The study – published in the journal Contraception – followed 22,785 women using the Natural Cycle smartphone app over 12 months, finding it to be 99 per cent effective under “perfect” use and 93 per cent effective under “typical” use. This is compared with 91 per cent effectiveness under "typical use" for the pill.
The application, which is approved in the EU as a contraceptive, asks the user to digitally record their body temperature each morning to produce an algorithm that predicts the days when they’ll be most fertile. Women are advised to abstain or use a condom during these ‘red days’ to avoid falling pregnant.
It's already used by over 380,000 women worldwide but some experts have expressed concerns over its reliability.
Dr Mary Jane Minkin, a professor of obstetrics, gynaecology and reproductive sciences at Yale University told LiveScience: "Don't rely on something like this."
Despite the significant scale of the study, Dr. Nathaniel DeNicola told LiveScience that the success rate seems unrealistically high and those results are only based on two clinical studies. In comparison, research on the pill, condom, and intrauterine devices, for example, goes back decades.