App for Preventing Pregnancy Gets FDA Marketing Approval. Is It Reliable?

A woman looking at her phone while in bed.
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A smartphone app for preventing pregnancy has just become the first of its kind to receive marketing approval from the U.S. Food and Drug Administration (FDA), but some experts are wary.

The app, called Natural Cycles, is essentially a high-tech version of the so-called rhythm method, also known as fertility awareness. It uses an algorithm to calculate the days of the month when a woman is most likely to be fertile and tells a woman to abstain from sex or to use protection (such as condoms) on these days.

The app requires that women take their temperature every morning, using a sensitive thermometer called a basal body thermometer, and enter the measurement into the app. These thermometers — which are provided to women who sign up for a yearly subscription to the app — can detect slight increases in body temperature around the time of ovulation. This data, along with information about a woman's menstrual cycle and factors such as how long sperm can survive in the woman's reproductive tract, is used to determine whether a woman is fertile, Natural Cycles says. (Typically, a woman can get pregnant on only about four or five days each month, according to the FDA.)

“Consumers are increasingly using digital health technologies to inform their everyday health decisions, and this new app can provide an effective method of contraception if it's used carefully and correctly," Dr. Terri Cornelison, assistant director for the health of women in the FDA's Center for Devices and Radiological Health, said in a statement released today (Aug. 10). "But women should know that no form of contraception works perfectly, so an unplanned pregnancy could still result from correct usage of this device." [Are You Pregnant? 10 Early Signs of Pregnancy]

Outside experts, however, are wary of using an app for pregnancy prevention.

"I don't feel that it can reliably take the place of [other] contraceptive method[s]," said Dr. Taraneh Shirazian, a gynecologist at NYU Langone Health. "I wouldn't encourage women to rush and use this app" until more research has been done on it, she said.

The company has done its own studies involving 15,570 women who used the app for an average of eight months, according to the FDA statement. If women used the app perfectly, meaning exactly as directed, about 2 in 100 women would get pregnant over the course of a year, the studies found. However, during a year of "typical use," which accounts for women sometimes not using the app as directed (for example, by having unprotected sex on a "fertile day"), about 7 in 100 women would get pregnant.

That would mean Natural Cycles is about as effective as birth control pills, which have a 9 percent failure rate during a year of typical use, according to the Centers for Disease Control and Prevention (CDC). And it would mean that the app is more effective than traditional fertility-awareness-based methods (such as basal-body-temperature monitoring without an app, or the calendar method), which have a failure rate of around 24 percent.

But Shirazian told Live Science that before comparisons can be made to other forms of birth control, there should be studies that compare the app head-to-head with other forms of birth control.

Dr. Nathaniel DeNicola, an assistant professor of obstetrics and gynecology at The George Washington University School of Medicine & Health Sciences, told Live Science in 2017 that research on other methods of contraception goes back decades, while data on the effectiveness of Natural Cycles comes from just a few studies.  

Still, Shirazian said many women are using apps to track their period and to estimate when they are fertile because they want to become pregnant. "I definitely think that there's a place for apps in terms of tracking fertility," she said.

The app is already approved in Europe. However, in July, the U.K.'s Advertising Standards Authority said it was investigating the app's marketing after reports that women became pregnant while using it, according to The Guardian.

And the app is also being investigated in Sweden after 37 women who used the app said they became pregnant.

However, Natural Cycles co-founder Raoul Scherwitzl told Business Insider in January that he wasn't surprised by the news out of Sweden, because the app is not 100 percent effective. "Just like with the pill, you have scenarios where women take the pill every day" and it's as reliable as possible and "scenarios where they don't take it every day" and the reliability decreases," Scherwitzl told Business Insider.

Natural Cycles says that, on average, users of the app receive about 10 "red days" each month, meaning they should abstain from sex or use protection. (The rest of the days are "green days," when the app says it's OK to have sex without protection.) Women may have more "red days" when they start using the app and fewer as the app gets to know their menstrual cycle.

According to the company, the app is recommended for women ages 20 to 40 who are in a stable relationship and are comfortable using protection on fertile days and taking their temperature in the morning.

Women should not use Natural Cycles if they are currently using hormonal birth control or if they have a medical condition in which becoming pregnant may lead to a significant risk for her or her fetus, according to the FDA. The app does not protect against sexually transmitted diseases.

Original article on Live Science.

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.