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Flo Health Research Reveals Menopause Makes Menstrual Cycles Longer and Less Predictable in Largest Study of its Kind

Findings underscore the need for enhanced menstrual health literacy among 45+ women facing cycle changes and symptoms during perimenopause

London, June 19, 2024Flo, the world's leading women's health app with 67 million global monthly active users, has unveiled the largest study of its kind, highlighting menstrual cycle patterns and their related symptoms across the ages. Published in the prestigious Scientific Reports of Nature Portfolio, this study draws from an unprecedented dataset of 19 million women and found that from age 45 onwards, women experience a dramatic increase in cycle length and variability. Prior to age 45, cycles progressively shorten, but as women approach menopause, their cycles become more erratic. This phenomenon has rarely been documented, primarily due to the frequent exclusion of this age group from menstrual cycle research. Conducted together with Dr. Lubna Pal, Professor of Obstetrics and Gynecology at the Yale School of Medicine, the study shows a holistic picture of the cycle changes that occur across the reproductive lifespan.

All women and people who menstruate will experience menopause in their lifetime, and yet, the symptoms and cycle patterns of this life stage are dramatically under-researched and overlooked. The lack of research into these subjects is extreme, with over 13 times fewer1 studies conducted on menopause compared to the subject of erectile dysfunction. Both women and medical practitioners feel the effects of this knowledge gap as a result. Physicians struggle to link women’s symptoms to menopause and prescribe appropriate treatment, while many women experience needless suffering.2 Flo's study aims to bridge this gap and enhance our understanding of perimenopause—the period of time leading up to confirmed menopause—and menopause itself.

The study investigated cycle and period length, irregular cycles, the most frequent menstrual-related symptoms, and how all of these factors change with age. With the help of 19 million users, Flo’s Science team found the following: 

  • The proportion of individuals with irregular cycles was highest in participants aged 51-55 (44.7%), and lowest in the 36-40 age group (28.3%).
  • Frequency of logging of cramps and acne is lower in older participants, while logs of headache, backache, stress and insomnia are higher.
  • The length of the menstrual cycle and menstrual cycle related symptoms show clear age associated patterns.
  • With increasing age, cycles get shorter and more variable until age 40-44. Periods are longest in women aged 18 - 25, with an average duration of 5.20 days. They then gradually get shorter and last, on average, only 5.06 days in women aged 41 to 45. After that, periods become longer again, but — importantly — they also become much more variable in length than in any other age group, indicating transition toward menopause.
  • Irregular cycles were most common among older women with nearly half of women aged 51-55 and nearly 1 in 3 aged 46-50 reporting cycle irregularity. This is in line with expectations as cycles become less regular during perimenopause.
  • Across all ages users experienced similar common symptoms, with cramps being the most common symptom logged. Also in the top three were tender breasts and fatigue, but only up to the age of 45, when headache took the place of fatigue.
  • With age, headache, backache, stress and insomnia were logged more often, as was happy mood, which peaked at age 50. Mood swings were highest among youngest and oldest women. 

Adam Cunningham, Ph.D., Senior Research Scientist on Flo’s Science Team and lead study author, said: “It was surprising how little research there is about women’s cycles and symptoms, with most research stopping at 40 or 45 years of age. At Flo, we are in a prime position to help address this knowledge gap given that we have the largest dataset when it comes to women's menstrual cycle patterns and symptoms. Advancing our understanding of female reproductive health is a core part of our mission and with this research we are one step closer to closing this knowledge gap.” 

Dr. Lubna Pal, Professor of Obstetrics and Gynecology at the Yale School of Medicine, added: “The importance of this study lies in the chronicling of menstrual cycle and symptom data for a large and diverse population of women spanning in age from early adulthood into perimenopausal years. Findings from this epidemiological approach based on real life data allow a more comprehensive perspective on the prevalence of menstruation related phenomenon, and if and how these may vary across stages of reproductive aging. The wide-ranging populations’ perspectives offered in this study can help enhance population awareness of what symptoms, if being experienced by a majority, could even be construed as “norm”, may even help lessen the trepidations and stigma attached to aging, and can enhance preparedness of healthcare givers in their approach to enquiry, assessment and efforts at optimizing care of women across the lifespan.”

In line with Flo’s Health mission of building a better future for female health, Flo’s Science team is helping close the gender medical research gap and improve the day-to-day lives of women globally by using invaluable anonymised data to deepen the understanding of women’s health. In addition to its work on reproductive aging, Flo Health’s Science team are researching topics such as menstrual literacy on the global scale, women's health related reproductive conditions, sexual health including female orgasms, pregnancy, perimenopause and menopause. For more information on the latest research from Flo Health, head to the Science and Research page.

About Flo Health: Flo Health is the #1 app in the Health & Fitness category; it is the #1 OB-GYN-recommended app for period and cycle tracking based on a 2021 survey among 500 US OB-GYNs. Over 380 million people have downloaded Flo, and 67 million use it monthly. With over 120 medical experts, Flo supports women and people who menstruate during their entire reproductive lives. It provides curated cycle and ovulation tracking, personalized health insights, expert tips, and a fully closed community for users to share their questions and concerns. As part of its mission to build a better future for female health, Flo's Pass it on Project aims to improve health literacy by providing up to 1 billion women in need with free access to Flo Premium on Android devicesFlo prioritizes safety and focuses on being the most trusted digital source for​ ​women’s health information. Flo Health’s Anonymous Mode feature was named a finalist for Fast Company’s 2023 World Changing Ideas Awards in the Rapid Response category as part of the company's commitment to privacy. For more information, please visit


  1. 666 papers available describing menopause symptoms compared to  8,717 papers on the subject of erectile dysfunction - according to search results on Pubmed: and