Do menstrual cycles synchronise?

There is no simple answer to this question. The suggestion that menstrual cycles synchronise was first published in 1971¹ by Martha McClintock. Since then, several studies have been conducted to replicate the findings, with some failing² and some succeeding³  to do so. According to a 2017 pilot study⁴ conducted by a period-tracking app company, cycles are actually less likely to sync as time progresses. Mathematical analyses have suggested that overlap of menstrual cycles is just a case of statistical probability.

To learn more, read this 2017 article⁵ by Oxford associate professor Alexandra Alvergnes.

References:

1. McClintock, M. (1971). Menstrual Synchrony and Suppression. Nature, 229.
2. Ziomkiewicz, A. (2006). Menstrual Synchrony: Fact or Artifact? Human Nature, 17(4), pp. 419-432.
3. Weller, A. & Weller, L. (May, 1993). Menstrual synchrony between mothers and daughters and between roommates. Physiology & Behavior, 53 (5), pp. 943-949.
4. Clue Period Tracker (2016). Do menstrual cycles sync? Unlikely, finds Clue data.
5. Alvergne, A. (July 14, 2016). Do women’s periods really synch when they spend time together? The Conversation.