If you’ve had your period for a number of years, you might notice that it’s not the same every month. Your cycle length might change, and you may notice that your symptoms vary. Knowing what to expect can help you understand your body better.
So how might your cycle change in your mid-30s and 40s? And what might happen once you hit the perimenopause years?
In our latest research study, and with the help of millions of Flo users, we investigated how your menstrual cycle pattern may change and how this is linked to age.
This study has been published in the scientific journal Scientific Reports, part of the prestigious Nature Portfolio publishing group.
What did we do?
Over 19 million members of the Flo community, aged between 18 and 55, helped us with this research. This makes it the largest study of its kind. Until now, most studies have only included women up to the age of 45. This leaves a significant gap in knowledge about the cycles, periods, and symptoms of women beyond this age.
Adam Cunningham, PhD, 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, and most research stops at 40 or 45.”
“Given that we have the largest dataset about women’s menstrual cycle patterns and symptoms at Flo, we wanted to rise to this challenge and provide much-needed data about women’s experiences, particularly in the over-45 age group,” Adam added.
So, Adam and the science team at Flo — along with Dr. Lubna Pal, professor of obstetrics and gynecology at Yale School of Medicine as well as a member of Flo’s Scientific Advisory Board — looked at the menstrual cycles and related symptoms logged by over 19 million Flo app members, including 448,910 women aged 46 to 55.
They investigated cycle length and period length by age, irregular cycles, the most frequent menstrual-related symptoms, and how all of these factors change with age.
What did we find?
So, you might be curious how your cycle might change over time and what this could mean for you. We found that the average length of women’s cycles changed with age. Specifically, we saw that cycles get slightly longer from age 18 to around 21 to 22. Cycles are the longest at this age and last, on average, 29 days.
Between the ages of 22 and 45, cycles gradually get shorter by around two days. After age 45, they become longer again. So, if you notice that your cycle has changed as you’ve gotten older, you’re far from alone.
How much a woman’s cycle length varies also changes with age. In 18 to 25-year-olds, it’s normal for cycles to differ by around 4.1 days from cycle to cycle. Cycles get more regular around ages 36 to 40, after which cycle length can start to vary greatly, by around 6.5 days from cycle to cycle in women aged 5 to 55.
Nearly half of women aged 51 to 55 and nearly 1 in 3 aged 46 to 50 had irregular cycles, which is when the number of days between your periods changes a lot from month to month, according to ACOG. This is perhaps not surprising as cycles become less regular during perimenopause, which is the time leading up to menopause.
Irregular cycles were the least common in women aged 36 to 40, where just over 1 in 10 experienced them.
While changes to your cycle are often linked to perimenopause, our study found that periods are longest in women aged 18 to 25, with an average duration of 5.2 days. Periods 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.
How did symptoms change?
Over 12 million of our members logged symptoms in the Flo app, and we found that these varied by age.
Cramps were the most common symptom logged by members of any age. 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.
Older users were less likely to log that they’d experienced cramping or acne around the time of their period. Headaches and backaches were more common among these users. In contrast, logging of tender breasts and fatigue was highest in the late 20s and early 30s.
The Flo community didn’t just log physical symptoms. With age, stress and insomnia were logged more often, as was a happy mood, which peaked at age 50. Mood swings were highest in our youngest and oldest members.
Bloating was by far the most commonly logged digestive symptom in all age groups. But, constipation was noticeably more common in older members.
What do our findings mean?
Dr. Lubna Pal said: “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 phenomena 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 health care givers in their approach to inquiry, assessment, and efforts at optimizing care of women across the lifespan.”
Without our Flo app members, this research would not have been possible. Through logging symptoms, they’ve helped us build a clearer picture of how cycles can change over time.
So, on behalf of the science team at Flo, thank you!
Your data and the research that it has become part of empower women and people who menstruate to better understand their own bodies and their health and what to expect from their menstrual cycle — right now and as they get older.
The published study can be found here: https://www.nature.com/articles/s41598-024-60373-3
