Would you trust an app to tell you if you’re fertile? Because it might be the future

Katherine spends 30 seconds each morning with a thermometer under her tongue. She takes her temperature and notes the result in an app on her phone. After a minute, her screen will beam one of two colours: crimson or bright emerald. The latter lets her know that she isn’t fertile. The former means that she is, and ought to use protection if she’s having sex that day. The 30-year-old is using Natural Cycles; the first birth control app cleared by America’s FDA. Think of it working like a standard period-tracker app, only powered by a very personal kind of algorithm.

Natural Cycles allows its users to either plan a pregnancy or prevent it, with prevention the most popular use among young women. There are a few intricacies (and disclaimers) about the app you should know about first, though. A user’s basal temperature – or the warmth of the body when it is fully at rest – must be recorded as soon as they wake up each morning. That means no snoozing your alarm. You can’t have a drink, leave your bed, or even move from your pillow before taking a reading. What’s more, the app advises users to skip submitting a reading if they have consumed alcohol the night before and feel hungover. Or if they feel unwell, or even if they wake up two hours earlier or later than usual.

The mobile app, which costs £59.99 per year or £8.99 per month, was certified in the European Union in 2017. In the UK, however, the NHS does not recommend the app as a birth control method. Natural Cycles claims to be 98 per cent effective at preventing pregnancy with perfect use, and 93 per cent effective with average use. Currently, it has 2 million users worldwide, with more likely coming: it’s being rolled out globally amid endorsements from a host of influencers. You probably won’t have missed advertisements for it on your Instagram or TikTok feeds lately.

Recent I’m a Celebrity... Get Me Out of Here contestant Olivia Attwood has promoted Natural Cycles, along with The Only Way is Essex’s Amber Turner and Married at First Sight’s Jessika Power. A common thread among this advertising is that the influencer will reference the unifying belief held among women who have used birth control before: hormones are rubbish. Horror stories about painful IUD coil installations, never-ending periods and contraceptive pill-induced mood swings are commonplace. “When I was younger, I tried so many pills,” Attwood wrote in her promotional post for the app. “For me it was awful, I had mood swings, migraines. I tried other options as well but found it uncomfortable. So, when I found @naturalcycles I was like – oh my God, this is like the golden ticket.”

Jana Abelovska, a superintendent pharmacist at Click Pharmacy, explains that more young women are rejecting traditional hormonal birth control options because they’re fed up with the side effects. Common contraceptives including the IUD coil or combined pill can cause a range of difficulties, such as headaches, mood swings, weight gain, acne and nausea. “Hormonal contraceptives [like the IUD coil or combined pill] can even lead to increased blood pressure and a decreased sex drive,” Abelovska adds. For many Natural Cycles users, the app seems like a much-needed alternative.

Katherine started receiving targeted adverts for Natural Cycles on her Instagram feed last year. Like Attwood, she decided to try the app after difficult experiences with the contraceptive pill. “I had been pumping hormones into my body for over 12 years and decided maybe it was time for a break,” she tells me. She says her experience has been positive. “[Natural Cycles] has made me more in tune with my body. I now notice the difference in my stomach, like bloating [before my period], and pains in my breasts and ovaries.”

There is a risk, though, that such effusive social media marketing could be misleading when it comes to the app’s effectiveness. Nic, 25, used Natural Cycles for six months until she fell pregnant and had to seek an abortion. “I really liked the idea of Natural Cycles,” she tells me, “but after I had an abortion, which was a tragic process for me, I wouldn’t go back to the app.”

Nic decided to ditch hormonal birth control after a decade of taking microgynon, or the combined contraceptive pill. She says it affected her mental health so intensely that she felt like a different person. An IUD coil was similarly unhelpful, and made her period “irregular”, she says. Natural Cycles seemed like the only option she had left. Though Nic admits that she wasn’t feeding the Natural Cycles algorithm as accurately or as consistently as she should have been, she found the process challenging, particularly compared to swallowing a tiny pill each day. “The whole thing is tricky,” she says. “Taking your temperature has to be the first thing you do when you wake up and you have to record it at that moment.” A slightly touch-and-go approach to fertility seems in-built.

A British Medical Journal open paper published in 2018 by scientists working with Natural Cycles found that usage of the app was most successful for people who’d shifted from less effective methods – those include condoms, which are approximately 87 per cent effective with typical use. Fertility expert Elizabeth King recommends that people trying to prevent pregnancy using Natural Cycles should also use condoms just in case “the algorithm isn’t exact”. She suggests that if a person is logging accurate information correctly, this method of fertility awareness can be effective for many people. “[But] if it’s your only form of birth control, I wouldn’t say the app is 100 per cent effective.”

Chief pharmacist Abelovska agrees, adding that the body’s basal temperature must be taken carefully for the algorithm to be correct, and for the app’s result to be effective. She encourages users to use condoms, too, for extra protection. “If users miss a temperature reading close to their predicted fertility window, barrier contraception, such as condoms, should be used to avoid accidental pregnancy.”

In a statement, a representative for Natural Cycles said that the app’s “real-life effectiveness rates remain in line with our published rates. I can also confirm that the method failure rate of our algorithm assigning a green day when a user is fertile is 0.5 per cent. This means less than one out of 100 women becomes pregnant due to this reason. We are proud of this effectiveness, which is regularly audited as a medical device, and deem it high.”

Will we see apps like Natural Cycles become widely approved and administered as a form of birth control? King doesn’t think so. She believes that healthcare professionals will refrain from recommending fertility awareness methods, primarily due to how difficult it is for people to track their cycle and temperature every day. “From a healthcare perspective,” she says, “it’s easier to go to the traditional form of birth control like the pill or hormonal options.”

Methods of birth control do not come without caveats. No form of contraception, unfortunately, will ever be 100 per cent effective or without side effects. But Natural Cycles, despite its vaguely dystopian optics, isn’t as eerie as it might seem. If anything, it’s little more than a digitised version of the “fertility awareness method” – or arguably the oldest contraceptive method in the book, one that existed long before condoms or coils were invented. It remains to be seen, though, whether users will love it enough to make inputting data while prone and groggy a regular part of their daily ritual.

This article was amended on January 30 to change a reference to the app being approved by the FDA. It is not approved, but ‘cleared’. It was further amended on January 31 to revise a quote from Jana Abelovska and remove a reference to the app’s algorithm having to correct itself, and to include the fact that a reading should be excluded if the user feels hungover, rather than if they have consumed alcohol the night before.