Natural Cycles will announce its sixth FDA clearance today, covering a next-generation algorithm trained on tens of millions of real-world fertility data points. The company built the first birth control app the FDA ever cleared.

Here is what the announcement leaves out. Three of the women behind that clearance are particle physicists who worked on the Nobel Prize-winning discovery of the Higgs boson at CERN.

That detail is not a quirky origin story. It is an argument about what women's health research has been missing, and about who decided to fix it. The gender data gap did not close because medicine finally got around to it. It closed, in this one narrow place, because a handful of women, who knew how to interrogate enormous datasets, got tired of waiting.

Why A Particle Physicist Solved A Problem Doctors Had Not

The temperature method predates the app by decades. Women measured basal body temperature and applied rudimentary rules by hand, which made the whole enterprise error-prone and easy to dismiss.

Elina Berglund Scherwitzl, who co-founded Natural Cycles in 2013, thinks the reason nobody fixed it sooner comes down to training. "Why a particle physicist like myself was able to do that rather than a physician is because we are trained in data and algorithms and statistics, while a physician is trained in understanding how the body works," she told me.

An algorithm can weigh previous cycles, illness, and a user's history on hormonal contraception, then separate a genuine ovulation signal from noise. A person reading a paper chart cannot.

Berglund Scherwitzl arose in a discipline where the evidentiary bar is five standard deviations. Medicine typically works at three. Ask her whether women should trust software with something this consequential, and she inverts the question, "For me to trust an algorithm that has so much data behind it is almost more reassuring than trusting a person and their personal judgment."

Her First Users Were Her Colleagues At CERN

The earliest version ran on published cycle research and Berglund Scherwitzl's own temperature readings. The first users after her were the women she worked alongside at the Large Hadron Collider, the world’s largest and most powerful particle accelerator, located at CERN.

One of them, Magda Armbruster, was her PhD student on the Higgs team. Armbruster now runs product at Natural Cycles. Eleonora Benhar Noccioli, another CERN physicist, leads science and data. Armbruster started on her team before moving over to product.

This is not a hiring accident. Berglund Scherwitzl spent years recruiting Armbruster, and other CERN physicists have since followed suit, joining the company.

Benhar Noccioli describes the transfer as smaller than it sounds. "At CERN, I learned to question assumptions, look carefully for bias, and let the data guide the conclusions rather than the other way around," she wrote in response to my questions. Hormones fluctuate across the cycle and, for a long time, that complexity became a reason to exclude women from research rather than study them more carefully.

Armbruster applies the same discipline to product decisions. "It's easy to fall in love with an interesting idea, but 'interesting' isn't evidence. We validate before we commit," she noted.

The women's health data gap is not merely an absence of information. It is an absence of people willing to treat that information as worth the trouble.

What Clinicians See That The Algorithm Alone Cannot

Physics rigor gets you an algorithm. It does not get you a product in which women recognize themselves. That required clinicians, and Natural Cycles recruited two who approach the problem from opposite ends.

A Diagnosis The Doctor Missed In Herself

Kerry Krauss is a board-certified OB-GYN. She has lived with PMOS, formerly known as PCOS, since her teens, and it still took her years to recognize what was happening in her own body.

She came to Natural Cycles as a patient before she became its senior medical advisor. Tracking revealed she was not consistently ovulating, even in months when her cycles looked unremarkable from the outside.

"It reinforced something I now tell my patients every day: Your cycle is a vital sign," Krauss wrote. She is blunt about how common her experience is, "Many women with PMOS spend years trying to understand what's happening to their bodies before they finally get answers. I know that feeling because I've lived it myself."

30 Years Of Patients And 10-Minute Appointments

Dr. Semiya Aziz has spent nearly three decades as a general practitioner (GP) in the National Health Service (NHS), the publicly funded healthcare system in the United Kingdom, and in private practice. She left to found her own clinic, Say GP, because the system kept failing the women in front of her.

Her vantage point is the opposite of a specialist's. "I've learned that the menstrual cycle is rarely just about periods. It is often one of the earliest indicators of what is happening across a woman's overall health," she observed.

In a 10-minute appointment, a woman is asked to reconstruct months of symptoms from memory. Aziz argues the data changes the nature of the conversation entirely. "What is most powerful is that the data validates lived experience. Many women often arrive having felt dismissed or told that their symptoms are 'normal.'"

Six FDA Clearances And The Moat They Built

Digital contraception's other players largely positioned themselves as wellness apps, which kept them clear of regulatory scrutiny. Berglund Scherwitzl went the other direction and pursued clearance, making Natural Cycles a Class II medical device.

The progression since is its own argument: De Novo clearance in 2018, Oura Ring integration in 2021, Apple Watch in 2023, a Predetermined Change Control Plan in 2024, over-the-counter and prescription availability in 2025, and this week's algorithm clearance. The app is 98% effective with perfect use and 93% with typical use, which puts it in the same category as the combined pill.

What Temperature Can And Cannot Measure

That standard now faces a forward test. Days before Natural Cycles' clearance announcement, Ida Tin, who coined the term “femtech,” launched a €40 million challenge to build biosensors that read hormones continuously, arguing the molecules have “stayed in a black box.”

The initiative explicitly disqualifies proxy signals, such as skin temperature, from the SPRIND Continuous Hormone Monitoring Challenge. The exclusion shouldn’t be taken as an indication that certain biomarkers cannot be used to infer fertility. Natural Cycles has built six clearances on exactly that proxy, and Berglund Scherwitzl. Temperature, she says, is “a remarkably powerful biomarker because it reflects the body's physiological response to progesterone after ovulation.” It captures where a woman is in her cycle without measuring hormone levels directly.

“I don't think this is an either-or conversation,” Berglund Scherwitzl says, adding that a technology has to be “practical, affordable, and convenient enough for women to use in everyday life,” not merely possible. If continuous monitoring clears that bar, she is ready to fold it in. Natural Cycles, she notes, “has never been about one specific biomarker,” and the company is already studying whether estrogen could flag the start of the fertile window. The physicist who trusts rigorously built algorithms is, characteristically, waiting on the evidence.

Natural Cycles is not alone. Clue’s period-tracking app cleared the FDA in 2021. Tin founded Clue. The company used an abbreviated pathway, citing Natural Cycles as its predicate device.

One of the papers supporting Natural Cycles’ latest clearance is the company's thirtieth peer-reviewed study. Krauss frames the milestone as a test the category has to keep passing. This clearance "demonstrates how advances in AI and machine learning can improve the user experience while preserving the scientific rigor expected of a regulated medical device."

Women Are No Longer Passive Recipients Of Care

The interesting question is not whether an app can prevent pregnancy. It is about who gets to hold information about a woman's body and what she is permitted to do with it.

Aziz sees the answer changing in her exam room. "Women are no longer willing to be passive recipients of care; they want to understand what is happening in their bodies, recognize patterns, and be active participants in decisions about fertility, hormones, perimenopause, menopause, and beyond," she observes. Interestingly, women are willing to provide their data to women’s health companies because women trust these companies.

Six clearances took the better part of a decade. The women who earned them were told, in effect, that the question was too complicated to answer. They ran the numbers anyway.