A new study strongly suggests that the possibility that a group of women who are friends and/or living together will eventually develop “menstrual synchrony,” that is, have their menstrual cycles sync up over time, is a myth. The type of biological bonding women sometimes feel when it seems as if their menstrual cycles have synched might result in a closeness above and beyond what men who are friends experience, but a new study based on data from the period-tracking app Clue and researchers at the University of Oxford has strongly suggested the idea that menstrual cycles of female friends will eventually sync up has no scientific foundation, period.
Allure Magazine reported that menstrual synchrony was the subject of a study by researchers from the University of Oxford who decided to re-examine the conclusions of a 1971 study. The study had suggested that an ‘alpha uterus’ existed, one that had enough hormonal power that it was capable of influencing a nearby, less dominant uterus to ovulate and menstruate at the same time it did. This study’s conclusions became widely spread around the world, with researchers suggesting the supposed menstrual synchrony that resulted having “to do with mating season,” by placing all women, except a dominant one, “sexually out of commission at the same time.”
According to SheKnows.com, the 1971 study was conducted by “psychologist Martha McClintock.” McCintock tracked “135 college students living in the same dorm.” She found what she believed was “strong evidence of period synchronization — particularly in terms of the participants’ cycle start dates.”
The period-tracking app, Clue, looked at a wide variety of relationships between 360 pairs of women who volunteered for the study. These relationships included siblings, mothers and daughters, roommates, partners, friends, and colleagues. The researchers at the University of Oxford, using the Clue app, “gathered data about the timing of the pairs’ periods over three consecutive menstrual cycles.”
Cosmopolitan.com reported that “this particular period syncing study is the largest of its kind.” By the end of the three consecutive menstrual cycles, the scientists at the University of Oxford who conducted the study discovered that “period syncing is more coincidence than it is a sign of bloody feminine bonding.”
Allure Magazine reported that the researchers “also took into account whether pairs lived together.” They eliminated from consideration in the study who were artificially adjusting their cycle by “using hormonal birth control.”
The results of the study undertaken by researchers at the University of Oxford were that by the end of three successive cycles, the menstrual cycles of 273 of the 360 pairs were farther apart than they were at the beginning of the study. In addition, the gap between cycles narrowed and got closer together for only 79 pairs.
At the start of the study on menstrual synchrony, the difference between all pairs and their cycles on average was 10 days. However, by the end of the study, the difference was larger on average at 38 days. Living together as roommates did not appear to have any effect on whether the cycles of these women synced or diverged.
The study found that 37 percent of the pairs of women whose menstrual cycles diverged “were roommates.” Only 24 percent of the pairs whose menstrual cycles synched up were, according to the study.
Marija Vlajic, Clue’s data scientist, told the Guardian she believed it was “very unlikely that cycle syncing is a real phenomenon.” Vlajic said, “Menstrual syncing amongst the sample we had did not exist.”
Clue’s data scientist said that some of the statistical tests they have done have found, like the study did conducted by scientists at the University of Oxford, “that the difference in cycles actually grows.” She said that did not mean that the pairs of women being studied “go out of sync — it means they were never in sync in the first place.”
The new study by the people behind the Clue app and researchers at the University of Oxford strongly suggests that, despite the findings of a 1971 study, menstrual synchrony is a myth. Every menstruating person “has a different cycle length.” A person’s cycle length can change from month to month, and possibly “changes several times in a year.” At some point during any year, a person’s menstrual cycle is “bound to align from time to time,” with some other female who might be a friend or family member, but when they do, “it’s just pure coincidence.”
By John Samuels