Menstrual cycle: influence of circalunar and circaseptan rhythms

The ovarian cycle has a well-established circa-monthly rhythm, but the mechanisms involved in its regularity are unknown. Is the rhythmicity determined by an endogenous clock or by other internal or external processes?

Using two large epidemiological databases (26,912 cycles from 2,303 European women and 4,786 cycles from 721 North American women) analyzed using circular statistics, we show that the rhythmic characteristics of the menstrual cycle are more likely to be explained by a clock-like endogenous entrainment mechanism than by any other internal or external process. We also show that the menstrual cycle is weakly but significantly influenced by the 29.5-day lunar cycle, and that the phase angle between the two cycles differs between the European and North American populations.

Given the need to find effective treatments for subfertility in women, our results must be confirmed in larger populations, with the aim of being able to assess whether chronobiological approaches aimed at optimizing the synchronization of the ovulatory cycle can be considered in clinical practice.