Lifespan Characterization of Chaotic Dynamics in Menstruation.

In previous work, we found evidence that chaotic dynamics characterize the human menstrual cycle. Here, we examine chaotic dynamics in menstruation year-by-year over the lifespan, with special attention to later life. Using data in the Tremin research program archives, lifelong menstrual cycle histories known for 143 subjects beginning at about age 20 through the final menstrual period (FMP) provided data for time series analysis. Cycle lengths were aggregated and analyzed by year prior to the FMP. Time series data was analyzed with procedures developed by Grassberger-Procaccia and by Judd, and the results summarized by a new measure defined herein, the inter-event correlation parameter (Icp). The menstrual cycle was characterized by chaotic dynamics rather than disorder or randomness throughout life until the FMP. Plots of the Icp versus the number of years prior to the final menstrual period showed a small increase approximately 17 years prior to the final menstrual period and a large monotonic decrease during the last 5-8 years before the final menstrual period. The shifts in Icp correspond in time to significant phenomena identified in menstruation research. Assumptions underlying the analysis are discussed in the article. Possible implications of these findings to paradigms of menopause are discussed.