A new statistical approach demonstrated menstrual patterns during the menopausal transition did not vary by age at...

To describe population mean, variance, and correlation of cycle length across the life span and by age at menopause and age at menarche using a new statistical approach.

Data from the Tremin Trust (n=997), a prospective menstrual diary study, was analyzed. Marginal models with generalized estimating equations were used to describe changes in menstrual parameters across the reproductive life span.

During the menopausal transition, the increase in standard deviation preceded that in mean by 2 to 6 years. Although beginning earlier in women with earlier menopause, increases in mean and variance for women with different ages at menopause were parallel. Women with later menopause had longer cycles throughout life and longer, more variable cycles during the transition.

The transition from late reproductive life to early menopausal transition appears to begin in the late thirties when variability of cycle length increases. Patterns of change in menstrual function during the menopausal transition do not differ by age at menopause; thus, differences in age at menopause are likely to reflect changes in the timing and not changes in the process of ovarian senescence, at least for the normative ages of menopause.