I don't know about scientific research, but my personal research says yes every time. Whenever I have a girl roommate or spend much time with another girl, our periods always come together. This never fails. I even had a friend who rarely had regular periods and would often go months without one. When we started living together, it was like clockwork. She would always start the day after me.

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I am 50 now and was looking for info on menstrual synchrony out of curiosity after it came up in discussion. I spent all my senior school years in a boarding school and at the beginning of each year your dorm location and dorm mates was posted on the front door of the main Boarding House. The dorms varied in beds from 2 to 8. Without fail around 2nd term (4 months into the year) most or all of us in the dorm had synchronised to within a few days of each other. This happened for 6 years. Without the internet to answer our question why....we simply took it for granted.

Many years later at 39yrs of age and having settled in one place for the first time since school, I experienced it once again when my best friend and I "synchronised". We worked together, practically lived together and supported each other through a bad time ...and we also never questioned it. It remained the same even after my partial hysterectomy ! Although I no longer had the period, my ovaries continued to work. When I moved away after 8 years, we rang each other around that time, just for fun, to check if it was still the same...even as she began IVF!!. It only changed after my ovaries and tubes were removed 12 months later and her IVF programme alter her periods.

Regardless of the medical debate it was happenning 36 years ago. There were 300 girls at my boarding school.....and we all just took it for granted.