The FDA’s decision to clear German company Clue’s cycle tracking app for birth control has angered Swedish rival Natural Cycles.

Clue is a science-backed female health app used by 13 million people in over 190 countries. It has received FDA clearance for Clue Birth Control, an all-digital form of contraception that uses period tracking data to allow women to monitor their fertility and prevent pregnancy. Clue Birth Control is 92% effective with typical use and 97% effective with perfect use.

But rival Natural Cycles, which was the first birth control app to be cleared by the FDA back in 2018 and has been CE marked as a contraceptive medical device in Europe since 2017, is not happy.

“We’re aware of a period tracker recently receiving FDA clearance, meaning that it too can market itself as a contraceptive,” said Elina Berglund, CEO of Natural Cycles. “This clearance was granted as an abbreviated 510k that claims equivalence to Natural Cycles. As a leader within this field, we feel it’s our responsibility to uphold the highest standards and after our initial findings based on the FDA filing indicate a significant difference between Natural Cycles and this other product, including that this product is solely based on menstrual data and no other biomarker such as temperature. Our medical and research teams will be doing an independent analysis.”

But a statement from Clue said: “The fact that no daily temperature measurements, other clinical observations or hardware are required is a major innovation in user-friendliness as compared with other fertility awareness-based methods of contraception.”

Clue Birth Control algorithmically combines menstrual cycle data with a mathematical model to predict which days are high or low risk for pregnancy. After consulting Clue Birth Control, users can adapt their behaviour as necessary, for example by using condoms or avoiding sex that may result in pregnancy when the app indicates high risk.

Clue Birth Control will be available as a feature within the Clue app for eligible US-based users in 2021. Further countries will follow subject to the relevant regulatory approvals, as the contraceptive feature is a regulated medical device.

Clue Birth Control doesn’t require users to track anything other than their period start dates, and its smart technology estimates a more accurate high risk window than traditional methods based only on period data. As the algorithm learns about a woman’s cycle over time, the predictions become more personalised, and the high-risk window estimated to contain ovulation can become shorter.

To coincide with Clue’s becoming a regulated medical device company, there is a strengthening of the company’s senior team, with founder Ida Tin moving to the role of chairwoman of the board, and the promotion of Audrey Tsang, formerly Clue’s chief product officer, and Carrie Walter, formerly Clue’s general counsel, to co-CEOs.

In her prior role, Walter, who joined Clue from Freshfields’ international regulatory practice, was responsible for Clue’s FDA application and has overseen the company’s transition to a regulated company. Meanwhile, Tsang, who has led product strategy for global brands at scale, including at Pinterest and Yelp, led the development of the Clue Birth Control feature as part of her responsibility for Clue’s overall product portfolio.

Now that Clue is evolving from a health and lifestyle mobile app into a regulated, medical device-grade mobile app, together as Clue’s new Co-CEOs, Walter and Tsang will focus on bringing accessible birth control to many more people around the world.

Clue Birth Control is designed for contraception, and has been tested in a rigorous clinical trial for that purpose. To obtain FDA clearance to offer this feature, the US regulator examined not just the clinical trial, but subjected the entire app as well as Clue’s software development processes to scrutiny. Clue had to satisfy the FDA that its science was sound, and that its way of working was up to the standards expected of a medical device manufacturer.

According to a year-long, full-scale and representative independent clinical trial of more than 700 women conducted by researchers at the Institute for Reproductive Health (IRH) at Georgetown University, Clue Birth Control’s algorithm is 92% effective with typical use and 97% effective with perfect use when used exactly as directed. For comparison, the combined oral contraceptive pill is 93% effective with typical use and 99.7% effective with perfect use. Condoms alone are 87% effective with typical use and 98% effective with perfect use according to the Guttmacher Institute.

The IRH researchers collaborated with US-based Cycle Technologies, which developed an app called Dynamic Optimal Timing (Dot) to conduct the clinical trial. When Clue was looking for better fertility awareness to implement as a feature for the Clue app, it acquired the Dot algorithm and implemented the Dot app’s functionality in the Clue Birth Control feature.

“We could see that the contraceptive options out there simply weren’t good enough,” said Tin. “We wanted to utilise our strengths in cycle science and data science to upgrade traditional fertility awareness-based contraceptive methods and create a smart version, easy to use, powered by the technology in our pockets. We wanted a trustworthy and reliable alternative for women, one that is based on their own personal data, effective, has no side effects, and is hormone-free. We’re excited that we have FDA clearance for Clue Birth Control, an innovation in natural pregnancy prevention which we believe will prove a better and more convenient method for many people’s needs and lifestyles.”

Berlin-based Clue was founded in 2012. Built by a dedicated team of developers and data scientists, Clue has built algorithms to detect users’ unique patterns in the cycle-related symptoms they track. Clue is then able to provide personalised predictions based on the individual user’s data.

Clue has forged research collaborations with the Kinsey Institute, Stanford University, Columbia University, University of Washington and University of Oxford. Each research collaborator is vetted and selected by Clue to answer specific research questions of a non-commercial nature.

Clue is available in 15 languages – English, Spanish, Portuguese, German, French, Italian, Danish, Russian, Chinese (traditional and simplified), Japanese, Polish, Hindi, Korean and Turkish – and is on iOS, Android and Apple Watch. Clue users can also link their account to Apple’s HealthKit, enabling them to push the following data to Apple’s Health app: basal body temperature, cervical mucus quality, menstruation, ovulation test results, sexual activity, spotting and weight.

To date, Clue has raised over $30m. The company’s investors include Nokia Growth Partners, Union Square Ventures, Mosaic Ventures and FJ Labs, as well as start-up entrepreneurs from Spotify, Dropbox, SoundCloud and Toca Boca.