Lifelong menstrual histories are typically erratic and trending: a taxonomy.

OBJECTIVE: Menstrual cycles are composites of complex events; the data describing them are correspondingly rich. We seek to quantitatively represent menstrual histories from menarche to menopause and to evaluate the clinical belief that regular and stable cycle lengths are the most normative histories.
DESIGN: Using prospective data from the Tremin Trust, we classified the menstrual histories of 628 women as very stable (type I), stable but with greater variability in cycle lengths (type II), oscillating and erratic with a downward trend in cycle length (type III), oscillating and erratic with no downward trend in cycle length (type IV), or highly erratic and variable (type V). Classification criteria were created by examining basic summary statistics of menstrual cycle lengths. Specifically, we identified key features describing variability of median cycle length, the mean of the interquartile range, the consistency of the interquartile range, the slope of median cycle lengths, and the number of stable 5-year intervals between ages 15 and 45+.
RESULTS: We present the first characterization of full menstrual histories. Our taxonomy captures the essential features of menstrual bleeding patterns for a heterogeneous population. Persistently stable histories (types I and II) were seen in only 28% of the women; erratic histories (types III through V) characterized 72%. When examining all participants, significant differences were seen in age at menarche (P < 0.05), age at menopause (P < 0.01), and number of births (P < 0.01) between these stable and erratic groups.
CONCLUSIONS: Although clinicians have traditionally thought of "normal" menstrual histories as being regular and stable, the distribution of women in our five categories suggest that variable histories are most common. Clinically, these results may suggest the need for a paradigm shift in what gynecologists view as normal and abnormal menstrual cycle histories.