So how does it work?

Most women are fertile for a maximum of six days per cycle, with the fertility window opening around five days before ovulation and closing on the day of ovulation.

The app measures fertility by monitoring body temperature, which works as an indirect measure of the hormone levels in a woman's body. Users are required to measure their temperature every morning and input their score into the app, which can then calculate the days on which they are most fertile and therefore most likely to get pregnant. Once the temperature is inputted each day, the user will see either a green "not fertile" screen or a red "fertile" screen.

While there are already a number of apps on the market that claim to measure fertility, Natural Cycle's daily measurement of body temperature makes it uniquely reliable. The app's website claims it is "clinically tested and tailored for you" and promises to measure fertility and ovulation as well as providing a period tracker. By monitoring a user's temperature, it is also suitable for women who have irregular monthly cycles, as it does not focus on the traditional idea of a 28 day cycle.

The app can also map the progress of a pregnancy through a user's temperature, meaning it is can also work for pregnant women looking for an easy way to monitor their baby's development. It can also detect when a woman has had a miscarriage.

Is this the hormone-free contraceptive we've all been waiting for?