“While on hormonal birth control I noticed so many changes that I didn’t like mentally or physically,” says an enthusiastic young woman in an Instagram ad for Natural Cycles, which claims to be the world’s first FDA-cleared birth control app. “Ever since switching,” she gushes, “my health has only been on the up & up!”
Natural Cycles uses a proprietary algorithm and daily body temperature readings to track ovulation and identify fertile periods. For around $120 a year, the company aims to help users either achieve or avoid pregnancy—without the hormones present in birth control pills and many IUDs.
That pitch seems to be working: Natural Cycles’ customer base grew to more than 3 million in 2024. It’s one of the premier products in the booming market for “femtech,” app-based software with a focus on fertility and menstrual tracking and, increasingly, sexual satisfaction. (Consider the Lioness orgasm-tracking vibrator: “Don’t just masturbate. Masturbate smarter.”) The femtech industry is already valued at around $50 billion by market researchers and expected to be worth more than $100 billion by 2032.
While these companies’ fertility algorithms and app interfaces might be new, the technique of tracking ovulation to prevent pregnancy isn’t. The Catholic Church, which forbids most birth control, popularized “natural family planning” decades ago, and women have been using their menstrual cycles to inform their reproductive choices long before that.
Femtech’s appeal fits in with a rising tide of right-wing wellness messaging—the kind promoted by the anti-vaccine activist-turned-Trump health czar Robert F. Kennedy Jr., and pundit Candace Owens, who called birth control pills and IUDs “unnatural” in a YouTube video.
For all its promises to help women “naturally” control their fertility, femtech has one big problem: In order for the apps to work well, users must be meticulous in their temperature recordings. Even for the most diligent users, that can be tricky.
Margaret Polaneczky, an OB-GYN in New York, points out that ovulation is hard to predict—weight fluctuations, medications, or even moving to a new place can affect the timing of the menstrual cycle. Femtech apps also need users’ health to be excellent for accurate readings; having a cold can skew users’ body temperature enough to potentially throw off fertility estimations.
Given the many variables that affect the timing of menstruation, it’s not surprising that femtech birth control can be unreliable. One 2018 review study of 73 of the apps found that none accurately predicted ovulation. While Natural Cycles boasts a “perfect use” effectiveness of 98 percent, its “typical use” effectiveness is only 93 percent (IUDs and the Nexplanon implant are 99 percent effective, in comparison). Plus, these efficacy numbers for Natural Cycles are based on clinical studies carried out by the company on self-selecting individuals, rather than from randomized controlled trials.
“We feel like there should be an effective non-hormonal method,” said Elina Berglund Scherwitzl, co-founder of Natural Cycles. No contraceptive method, she argued, is “100 percent effective and there will unfortunately always be pregnancies, even if that’s the tough part of what we do.”
In 2018, the same year that Natural Cycles was approved by the FDA, the United Kingdom’s Advertising Standards Authority concluded that the app misled consumers about being “highly accurate” and a “clinically tested alternative to birth control.” In July 2018 researchers at the London School of Hygiene and Tropical Medicine published a study noting “Natural Cycles’ marketing materials ought to be entirely transparent” and more clear “about the limitations of their app and pregnancy risks.” A hospital in Stockholm even filed a complaint with the Swedish Medical Products Agency after 37 women who had been using Natural Cycles sought abortions after they unintentionally became pregnant.
Many femtech companies also don’t mention the health benefits users may be giving up when they ditch pills and IUDs. Hormonal IUDs like the Mirena can be used to treat and prevent endometrial and ovarian cancer. The birth control pill also reduces users’ relative risk of endometrial cancer by some 70 percent, with 12 years of use, and ovarian cancer by 50 percent with 15 years of use.
The privacy concerns are obvious, especially as some states have moved to criminalize abortion. Several femtech companies have faced criticism for allegedly sharing users’ data with third-party researchers and companies. And there’s potential that law enforcement could request data from period-tracking apps as evidence. For its part, Natural Cycles offers an anonymous setting option “if you need an extra layer of protection,” which separates any personal identification from a user’s fertility data—but this setting has to be manually turned on.
Despite the questions around efficacy and privacy, the femtech industry shows little sign of slowing. Last year, Natural Cycles closed a $55 million financing round, and formed a new partnership with J.P. Morgan. Its roster of products has expanded, too. Natural Cycles now offers “NC Follow Pregnancy” and “NC Postpartum,” a suite of subscriptions that could appeal to users for years to come.
Polaneczky, the OB-GYN, acknowledged that fertility apps might help people who can’t use hormonal birth control because of medical conditions or unwanted side effects. Yet, she cautions, you “have to be a certain person, I think, to do this well.” The problem? “My experience is that the majority of women,” she says, “are not that person.”
