Natural Cycles is a Swedish app that offers an alternative to birth control pills, using a thermometer and an algorithm.

The app was approved by the European Union as a digital contraceptive, and its largest subscription base is in the UK.

The startup raised $30 million to expand to the US, where it hopes to gain FDA approval.

CEO Elina Berglund Scherwitzl fears pushback from the American scientific community.

Natural Cycles has developed is a smartphone-enabled alternative to birth control methods such as contraceptive pills, coils and condoms.

In February, the Swedish startup’s app was the world’s first to be approved as a contraceptive, after receiving a go-ahead from the Medical Products Agency of Sweden.

This summer, the company's "digital contraceptive" also got EU-wide approval, clearing the way for European expansion.

The Natural Cycles app displayed on an iPhone. Natural Cycles/Facebook

Natural Cycles has now announced a $3 million Series B round led by EQT Ventures, with participation from existing investors Sunstone, E-ventures and Bonnier, reports TechCrunch. This follows a $6M Series A round from last year. The company has said it plans to raise additional funds before the end of 2017.

"It feels fantastic. With this money we will be able to take Natural Cycles to the next level,” said Elina Berglund Scherwitzl, cofounder and CTO, to Swedish tech site Breakit.

Natural Cycles offers a subscription product, which now has over 600,000 users across 160 countries. “75 percent use the app as a contraceptive, and the rest use it try and become pregnant,” Berglund Schewitzl told Breakit.

The U.K. recently surpassed Sweden as Natural Cycles' biggest market. Going forward, Berglund Schewitzl says, the company's goal is that almost all women between 20 and 40 in the U.K. will have heard about the app. Another big priority is the U.S., where Natural Cycles hopes to achieve certification by the FDA.

To use Natural Cycles, women take their temperature every morning and enter it into the app

An algorithm then determines the user's risk of getting pregnant from unprotected sex.

Natural Cycles' turnover last year was north of $2 million, a number it surpassed already a few months into 2017. Its biggest competitors include Kindara and Glow in the U.S., and Berlin-based Clue in Europe.

Earlier this year, Natural Cycles was part of a study which found it to be more effective than the contraceptive pill, with a 93 percent (out of 100) score on the Pearl Index under normal use.

However — as Natural Cycles admitted at the time — the study was not comprehensive enough to be able to say with certainly that digital contraceptives will rule the day.

Berglund Scherwitzland, who previously worked as a particle physicist at CERN, has said her team will likely face pushback from the scientific community for some time to come.

“Any [fertility awareness] app that makes efficacy claims should have been examined in a standard efficacy study,” says Victoria Jennings, director of the Institute for Reproductive Health at Georgetown University, to TechCrunch.

Berglund rejects the claim that the app’s users risk being misled by having it as an alternative alongside the pill, IUDs, and condoms.

“We try to be very clear in our communication that if you do use withdrawal [as a contraceptive method] on red days then your pregnancy probability is much higher.”

The average age of a Natural Cycles user is 29-years-old, whereas the renewal rate after a first year's subscription (which includes a free thermometer) currently stands at 60 per cent, reports TechCrunch.

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