The World's First Certified Contraceptive App

A fertility app that can help to prevent unwanted pregnancy.
21 March 2017

Interview with 

Raoul Scherwitzl, Natural Cycles


Using a mobile phone


Last month the fertility app Natural Cycles became the world's first app to be certified as a method of contraception. Chris Smith spoke to co -founder Raoul Scherwitzl...

Raoul - With Natural Cycles a woman measures her temperature in the morning then enters it into the app, and then the algorithm crunches the data and returns a “red” or a “green” day. On a red day there is a risk of pregnancy and the couple need to use protection or abstain, and on a green day there’s considered no risk of pregnancy so they are good to go.

Chris - Tell us, what is the physiology or the way the body works, the principle on which this is founded?

Raoul - The medical basis is actually a hundred years old. It’s known that after ovulation, the temperature rises because of an increase in progesterone and so by tracking your temperature what you can do is identify that ovulation has happened. If you take sperm survival into account and the ovulation day, you can compute the days where there is a risk of getting pregnant and the days where there’s not.

Chris - Does this work straight out of the box or does the person have to teach the machine about them. Because, obviously, everyone’s different and if you talk to different women they will say that, broadly, that their cycle is a month long, but it varies.

Raoul - Yeah, I would say that cycles are generally irregular, and the good thing with the algorithm that we’ve developed is that it adapts to every woman’s unique cycles. So the woman just needs to get started with measuring and Natural Cycles takes care of the rest.

Chris - Now when you say “get started,” as in how many cycles would a woman have to go through before she could rely on your tool?

Raoul - Oh, she can rely on the tool from day one. But the app, in the beginning, will be very conservative when it gives a green day because the algorithm simply doesn’t know yet whether the woman is fertile or not. So, in the beginning, she’s likely to start with red days, days where she needs to use protection and then. In the first cycle, generally, the algorithm finds the first ovulation and then gives green days for the rest of the cycle where she’s not fertile. That fraction of green days per month, or per cycle gradually increases over time and stabalises roughly after three cycles.

Chris - How many people have you tested it on?

Raoul - The app is being used by more than 200,000 women worldwide as of today, basically. It’s a lot of women using the app. The clinical studies that we have done, however, were done of 4,000 women using the app for a total of 2,000 years.

Chris - When you say 2,000 - as in 2,000 women years. So the number of people using it added up to the equivalent of 2,000 years of use?

Raoul - Exactly.

Chris - What’s it’s success rate? How reliable is this?

Raoul - Contraceptives effectiveness are generally measured in pearl index, so they tell how many women get pregnant in a year when using this certain contraceptive, and in our case it showed that seven women out of a hundred get pregnant in a year for all possible reasons; that’s a typical use pearl index. And five women out of a thousand get pregnant in a year because we give a wrong green day because the algorithm falsely attributed a green day within the fertile window.

These results are extremely promising it definitely already improves the use of natural family planning which, so far, has always been considered less effective. With the algorithm now and with the automation behind it it improves the use to the level where it becomes comparative to the contraceptive pill.

Chris - Now you say you’re the first app every to be certified for this use. I’m aware of many people that have published similar sorts of, or invented similar sorts of things in the past, so what sets you apart that enables you to get that certification?

Raoul - Contraception is a serious thing. It’s very important that you get that right and so if you want to bring an app onto the market for contraception, then you need to not just convince women of it, and doctors with it, but you also need to convince regulators that this is safe for the public to use. And, therefore, we underwent conformity assessment that you need to do if you want to bring a contraceptive product onto the market.

Chris - And in 30 seconds, if someone is interested in trying out this product, how do they find out more about it?

Raoul - They go to a website on or they download it from the app store.


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