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European regulators are ramping up their scrutiny of a controversial app that its backers hail as a side-effect-free alternative to hormonal birth control pills — and which the Food and Drug Administration in the U.S. just cleared last month.

The Swedish Medical Products Agency is set to release the findings of a monthslong investigation into the app, Natural Cycles, as soon as this week. Earlier this year, a spate of women in that country reported unintended pregnancies after using the app. Separately, the U.K.’s advertising regulator concluded on Aug. 29 that a 2017 Facebook advertisement for Natural Cycles that claimed the app was “highly accurate” was misleading. The company, which is headquartered in Sweden, had its app certified for use as contraception in Europe in 2017.


The app’s recent stumbles in Europe stand in contrast to its relatively smooth pathway through the FDA’s device approval process. Cleared on Aug. 10, an agency official called it an “effective method of contraception if it’s used carefully and correctly.”

The contrast may underscore the difficulty regulators across the globe face as they work to squeeze new and changing technologies through old protocols for clearing devices. In both Europe and the U.S., health care apps fall into an area defined by fuzzy lines. The FDA, which issued its first guidance for health-related smartphone apps in 2013, is actively developing health app-specific guidance and programs; the European Commission released a new Medical Device Regulation for smartphone apps in 2017.

Natural Cycles is one of a handful of products that helps people follow changes in their resting body temperature, known as the basal body temperature. That temperature shifts slightly after a woman’s ovary releases an egg, due to surges in the hormone progesterone.


Since eggs will only survive for about a day without fertilization, Natural Cycles uses that temperature to predict when users should abstain from sex or use another birth control method, like a condom, to avoid pregnancy. The exact algorithm the app uses hasn’t been made public.

Natural Cycles requires a $79 annual subscription or a $9.99 monthly payment; the annual subscription includes a thermometer.

About 2 to 3 percent of American women who use contraception use “fertility awareness-based methods” like Natural Cycles, according to a recent paper — and that number has increased over time. Just 1.1 percent of people reported using such methods in 2008. Some 900,000 people globally have downloaded the Natural Cycles app, according to the company’s website.

The scrutiny in Europe — and some of the skepticism — stems from just how easy it could be to misuse the app.

All methods of contraception have a failure rate. The FDA estimates Natural Cycles has a “typical-use” failure rate — the rate expected for those who use the app regularly, but not perfectly — of 6.5 percent. That’s actually lower than the comparable rates for birth control pill, which the CDC’s website puts around 9 percent. Condoms have a typical-use failure rate as high as 18 percent.

These failure rates may seem high — but that’s because each method affords plenty of opportunities to mess something up. People can forget to take a daily pill or put on a condom incorrectly or take temperature readings at the wrong time.

And, of course, they could just ignore the app — in fact, that’s the most common reason for failure, according to Dr. Rachel Peragallo Urrutia, an OB-GYN at UNC Health Care who has extensively researched the method’s effectiveness.

The method is “very susceptible to imperfect use,” she added. Urrutia’s salary is in part funded by an organization that backs contraception based on fertility awareness.

Irregular menstrual cycles can also make these methods more challenging for a person to use, as can certain conditions like polycystic ovary syndrome can create fluctuating hormone levels that mimic symptoms of fertility, Urrutia said. The app asks people if they have been diagnosed with one of these conditions when they enroll.

Even healthy people with regular cycles are encouraged to use a backup method when beginning a new method of birth control — and that’s no different for fertility awareness-based methods. One of Natural Cycles’ scientific advisers suggested using a second method of birth control for up to three months after beginning to use the app.

Natural Cycles’s potential susceptibility to misuse is what raised red flags in Sweden. More than 30 women using the app had reportedly sought an abortion at one hospital in Stockholm. Since beginning its investigation, the agency has been collecting data about how the company has tracked its app’s performance and effectiveness since releasing it and will be looking for any “shortcomings” as it decides what, if anything, needs to be done.

Compared to other birth control methods, a lot more uncertainty surrounds the failure rates associated with methods like Natural Cycles, noted Chelsea Polis, a senior research scientist at the Guttmacher Institute — there’s just not a lot of high-quality studies showing how effective (or ineffective) these methods are. (Polis has co-authored a paper with Urrutia.)

“I still am hoping for there to be continued clarification around what the most reliable typical use effectiveness rate is for Natural Cycles,” Polis said. “Whatever stems from this investigation needs to be folded in to the broader conversation.”

That conversation may need to include how apps are promoted. “The regulation around advertising for many of these methods is not very strong,” she said.

It’s not clear clear what, if any, effect the Swedish report’s findings would have in the United States. “We reached out to the Swedish authorities and feel that the information regarding the pregnancies in Sweden is consistent with our knowledge concerning the pregnancy risks associated with use of this device,” said FDA spokesperson Deborah Kotz in an email after the agency cleared the app. “An increase in the absolute numbers of unintended pregnancies is expected with a growing number of users.”

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