November 21, 2019
5 min read

Apple research app to begin tracking menstrual cycles for women’s health studies

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Apple recently announced that it will partner with the Harvard T.H. Chan School of Public Health and the NIH’s National Institute of Environmental Health Sciences to create the first long-term study on a large scale focused on menstrual cycles and gynecologic conditions. The Apple Women’s Health Study, using the capabilities of the Apple Watch, will inform screening and risk assessment of women’s health conditions, such as polycystic ovary syndrome, infertility, osteoporosis, pregnancy and menopausal transition.

“There are very well-established norms for ‘regular’ menstrual cycles, and women who get a sense of their normal menstrual cycle length will now be able to recognize departures from the norm, as well as from their norm, and may be able to use this as a tool to bring their system back into equilibrium,” Nanette Santoro, MD, professor and chair of reproductive endocrinology and infertility, department of obstetrics and gynecology at the University of Colorado Denver, told Endocrine Today. “The amount of data that will be forthcoming through this application should give us an even larger base from which to learn new and more subtle factors that relate to menstrual cycle length.”

Nanette Santoro

For the study, participants will be able to enroll via Apple’s Research app, to be available in late 2019, according to a press release from the company. The findings, which could potentially include hundreds of thousands of reproductive-age women, could help researchers to better understand cycle length across a large and diverse cohort as well as spark important conversations between women and their health care providers, according to experts.

The Apple study is part of a growing effort to provide women with digital tools to better track menses and reproductive health concerns. Hundreds of apps are now available to track cycle length, and researchers are only beginning to analyze the effect of tracking and recording such data while balancing issues of accuracy — a common complaint among users of period tracker apps — and data privacy concerns.

“A disruption in menstrual cycle length, or skipping menses, is an indication, usually, of an underlying endocrine problem,” Andrea Dunaif, MD, professor of molecular medicine and system chief of the division of endocrinology, diabetes and bone disease at the Icahn School of Medicine and Mount Sinai Health System, told Endocrine Today. “It is an indicator that needs to be further evaluated.”

The studies are being conducted with Apple’s ResearchKit technology, which drove the Apple Heart Study that showed that the Apple Watch could detect suspected atrial fibrillation.


‘Tidal wave of novel information’

In a study published in May 2017, Daniel A. Epstein, PhD, assistant professor in informatics at the University of California, Irvine, and colleagues collected and coded 2,000 reviews for the 12 most popular menstrual tracking apps on the iPhone App Store and Android Market (nine distinct apps; three were cross-platform). Researchers then surveyed 687 people to understand their practices around tracking menstrual cycles.

Andrea Dunaif

Survey results showed 313 (47%) participants used an app on their phone to track their menstrual cycle.

“Women track [menses] to better understand their bodies and mental states, to have materials prepared for their period, to predict ovulation, and/or to describe their menstrual cycle to their doctors,” Epstein and colleagues wrote. “These practices differ from the traditional personal informatics focus on tracking one’s behavior, rather than one’s experiences.”

In addition to serving as a diary of past periods, apps often use a woman’s average cycle length to predict when her next period will occur and when she is ovulating, the researchers wrote. This information is typically conveyed on the home screen of the app or sent in a push notification or email.

“Women often judge apps on the accuracy of these predictions,” the researchers wrote, noting that 302 app reviews mentioned how accurately the app predicted their cycle, with 65 reviewers describing apps as unhelpful due to inaccuracy.

Rebecca Thurston

In a study published in August, Jonathan R. Bull, PhD, a senior clinical research scientist at Natural Cycles Nordic AB in Stockholm, and colleagues assessed menstrual cycle characteristics observed from a database of more than 612,000 ovulatory cycles collected through the Natural Cycles app and investigated associations of menstrual cycle characteristics, such as menstruation, basal body temperature and luteinizing hormone, with cycle length, age and BMI. For a cohort of 124,648 users, mean cycle length was 29.3 days, mean follicular phase length was 16.9 days and the mean luteal phase length was 12.4 days. Mean cycle length decreased by 0.18 days and mean follicular phase length decreased by 0.19 days per year of age among women aged 25 to 45 years, according to the researchers, and the mean variation of cycle length per woman was 0.4 days or 14% higher in women with a BMI greater than 35 kg/m² relative to women with a BMI ranging from 18.5 kg/m² to 25 kg/m².

“The study demonstrated that a minority of women have 28-day menstrual cycles,” Dunaif, said. “We talk about 28 days as being the gold standard. These researchers showed cycles can vary in length and that there are age-related changes and BMI-related changes. It is transformative to the field. This is the beginning of a tidal wave of novel information about menstrual cycles and the kind of variety there are. Hopefully, it will allow women to seek care much sooner and to be interested in their health.”


Health and cycle length

Santoro said there are three common factors that tend to disrupt normal menstrual cycles: stress, which usually lengthens cycles; weight gain or weight loss, which also tends to lengthen cycles; and changes associated with early menopause or other rarer endocrine conditions, which can result in longer or shorter cycles. The amount a woman bleeds tends to be less important from an endocrine point of view than the fact that she does bleed and has a menstrual period at least once every 3 months, Santoro said.

“Menses that are more scarce may be related to health problems, such as risk for osteoporosis, and should be investigated,” Santoro said. “Menses that are very frequent, meaning more frequent than every 25 days, and bleeding that occurs between menstrual periods should also be investigated. These symptoms could signal gynecologic problems, such as fibroids or polyps of the uterus.”

Stephanie S. Faubion

Rebecca Thurston, PhD, professor of psychiatry, psychology and epidemiology at the University of Pittsburgh, said irregular or absent menses in a woman’s reproductive years can indicate a range of potential conditions that have implications for women’s health more broadly, including women’s bone, CV and brain health.

“In short, menstrual cycle information provides very important information about women’s health,” Thurston told Endocrine Today. “Assuming that the technology is reliable and has adequate protections for user privacy in place, this is a very important innovation in helping the research community further understand both the prevalence of menstrual disorders and the importance of these conditions to women’s health.”

Stephanie S. Faubion, MD, MBA, FACP, NCMP, IF, medical director of the North American Menopause Society and executive director and international medicine director of the office of women’s health at Mayo Clinic in Rochester, Minnesota, said big data gleaned from this type of study will help researchers identify associations that cannot be detected with smaller studies.

“Certainly, Apple has the capability to accomplish this ambitious goal,” Faubion told Endocrine Today. “I am hopeful that this will ultimately inform the clinical care of women beyond menstrual cycle tracking for fertility or menopause identification purposes.”

In addition to the Apple Women’s Health Study, the company announced the Apple Heart and Movement Study and the Apple Hearing Study, which will also be available through the new Research app. by Regina Schaffer


Disclosures: Thurston reports she has consulted for MAS Innovations, Procter & Gamble and Pfizer. Dunaif, Faubion and Santoro report no relevant financial disclosures.