Back in February, we brought you the news that Natural Cycles had become the first period-tracking app to be officially approved as a method of contraception. Now, a new study has found that not only does the ground-breaking tech startup work as a contraceptive – it’s actually as effective as the pill at preventing pregnancy.

Natural Cycles proved 99% effective in a recent study, published in the journal Contraception. Over 22,500 women with an average age of 29 were asked to use the app as their main form of contraception for one year, and to report back on whether it worked for them. Overall, the women logged details of almost 225,000 menstrual cycles into the app.

The app, which costs £40 a year, differs from other period-tracking apps because it asks women to record their body temperature every morning using a thermometer. This works as an indirect measure of hormone levels, allowing the app to calculate the days on which a user is most fertile (and therefore most likely to get pregnant).

On ‘green days’ in the app’s calendar, users are safe to have unprotected sex. On ‘red days’, women are at their most fertile and should use protection such as condoms.

The new study found that if used ‘perfectly’ – i.e. always using protection on red days - Natural Cycles’ effectiveness is 99%.

Most of the participants in the study didn’t quite manage to use the app perfectly, and didn’t use protection on red days. Even in these cases, however, Natural Cycles still proved to be a relatively trustworthy method of contraception: ‘typical’ use was found to lead to 93% effectiveness.

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This is much more reliable than other natural family planning methods, and even tops the pill, which is typically around 91% effective, according to NHS Choices.

While many women use the pill for years without any problems, many others experience negative side effects while on hormonal contraceptives. As a result, the news that Natural Cycles is just as effective as the pill is likely to be met with enthusiasm.

The app was developed by Elina Berglund – a former CERN particle physisict who co-discovered the Higgs Boson – alongside her husband, Raoul Scherwitzl. Berglund tells Wired that the app is not just used to prevent pregnancies; it is also used by women who want to track their fertility in the hopes of getting pregnant.

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“What we see in our data, which I find very promising, is younger women getting pregnant less when using the app even though they are more fertile, because they really don’t want to get pregnant,” she says. “Slightly older women are those that get pregnant the most using the app.”

Berglund suggests that this could be because older women may be more open to the possibility of getting pregnant, and therefore may not worry about using the app ‘perfectly’. She says that she would love to see women using Natural Cycles across all their menstruating years – using it as contraception first, then to help them plan for a pregnancy, and then after the baby is born. It can also help predict and plan for when period pains are likely to strike.

“People usually say what they like the most about the app is that it knows their body and helps them understand what’s going on inside,” she says.

Images: Natural Cycles / iStock