Variation in menstrual cycle length and cessation of menstruation in captive raised baboons.

Primatologists have recognized that non-humans undergo the menopause [Biol. Reprod. 68 (2003) 10], which is preceded by years of irregular cycles and decreased fecundity. The similarity of reproductive changes between humans and baboons suggests that the aging female baboon is a particularly promising model to study human menopause and changes that precede it. In an effort to provide an assessment of potential peri-menopausal changes in reproductive function in non-human primates, our goals were to determine if menstrual cycles become more variable with age and to identify the onset of changes consistent with peri-menopause and menopause in baboons. To accomplish these goals, we calculated means and variances for menstrual cycle lengths of females at ages 5, 10, 15, and 20 years and identified onset of menstrual cycle variability (peri-menopause) and cessation of menstruation (menopause). Mean cycle lengths were not significantly different, but significant heterogeneity of variances existed, with younger animals experiencing less variability than older animals. Mean ages of onset for the peri- and menopausal transitions were 18.89 and 26.34 years, respectively. These results provide evidence that captive aging female baboons experience menstrual cycle changes similar to peri- and menopausal women.