Elina Berglund helped find the Higgs boson particle. But when the Large Hadron Collider finished its first run in 2012, the Swedish particle physicist felt ready for a change. "It's impossible to top that," she says. "So I thought, why not try something completely different?"



That something was fertility app Natural Cycles. Berglund, 32, began working on the app while still at CERN (the European Organisation for Nuclear Research). "I wanted to give my body a break from the pill," she says, "but I couldn't find any good forms of natural birth control, so I wrote an algorithm for myself."



Berglund's algorithm - based on advanced statistical methods from her time at CERN - uses body temperature to determine fertility. After ovulation, increased levels of progesterone make women's bodies up to 0.45°C warmer. Input your daily temperature into her app, and by comparing the readings with those in its data set, it lets you know when you can have unprotected sex (shown as a green day in its calendar) and when to use contraception (shown as red).



Natural Cycles has conducted two clinical trials, the second of which analysed the data of more than 4,000 women aged 20-35. Over the course of one year, there were 143 unplanned pregnancies, ten of which occurred on green days, giving the app a 99.5 per cent efficacy rating - the same as the pill. Natural Cycles is currently the only app of its kind to be regulated as an approved medical device, putting it in the same category as condoms and IUDs - albeit in a different class.

Natural Cycles


Berglund's next aim? For it to be classified as a contraceptive, not a fertility monitor. "We are a natural alternative to the pill - with no side effects."

Critics have raised doubts about this claim. “Natural Cycles is not recommended to those who are very young or very keen to avoid a pregnancy, since there are other more effective methods,” says lead author Kristina Gemzell Danielsson, from Swedish medical institute Karolinska Institutet. “The efficacy is far below that of intrauterine contraception or implants, but similar to that of the pill when used in real life.”

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Writing for NHS Choices, medical data analysts Bazian noted that “an app like this helps to keep track of...when it would be better to abstain from unprotected sex,” but observed that “data was not collected to specifically answer this question and may not be fit for purpose.”

“It is important to notice that our study was a real-life study,” says Berglund, “which means the performance of Natural Cycles was assessed as close to reality as possible. In controlled clinical trials, the performance is always better because there is a lot of supervision from clinicians that remind for example women to take the pill, to use condoms, and so on.”

“It’s not a clinical trial but shows real-life performance,” agrees Danielson. Responding to observation that drop-out rates in the study were higher than with the pill, she says: “True, motivation is key. For many women this is not the best method. However for motivated women it can be an alternative.”


Natural Cycles can help women plan a pregnancy, as well as prevent one. Now Berglund is focusing on this aspect of the app, with a clinical study examining the factors that impact pregnancy, and a campaign that launches in the UK tomorrow: “#HappyPregnancy.” As part of the campaign, Natural Cycles is offering a refund to any woman who fails to conceive within nine months of use.

The app currently has 100,000 users paying £6.99 per month, and in June, the company received $6 million (£4.5m) in series A funding. So what comes next? “Many things!” says Berglund. “Expanding the team in the UK and internationally is a big focus for us as are the new clinical studies.”

To this end, Berglund recently hired another particle physicist from CERN, to analyse the data from the app. She hopes that, in this way, she can convince women in the security of her app. “It can be very scary, especially when it has to do with your body and your health,” she says. “We know we are dealing with women’s lives here and we take that very seriously.”