Associations with age at natural menopause in Blackfeet women.

This study seeks to determine the age at natural menopause and factors that may predict that age for Blackfeet women living on the reservation in Montana. Data were obtained from a probability sample of 150 women. Rates of surgical menopause among women who had experienced menopause were similar to those found in NHANES I for U.S. women. Median age at natural menopause by the status quo method (51.2 years) was comparable to that determined for other populations. Within the group of women who already had experienced natural menopause, age at menopause was associated in bivariate models with age at menarche (b = -0.83 +/- 0.44 years, P = 0.07), household income (b = 1.85 +/- 0.71 years, P = 0.01), "ever use" of birth control (b = 4.52 +/- 1.58 years, P = 0.008), "ever use" of oral contraceptives (b = 5.48 +/- 1.91 years, P = 0.007), current or recent unemployment (b = 4.75 +/- 1.97 years, P = 0.02), having been breastfed (b = -6.93 +/- 2.67 years), and educational attainment (ANOVA by tertiles of menopause age, mean 10.0 +/- 3.6 years of education for earliest, 13.0 +/- 2.2 years for latest, P = 0.04). In multivariate models, "ever use" of oral contraceptives, household income, and age at menarche remained significant predictors of age at menopause (R2 = 0.33-0.35, P = 0.002-0.004), with household income modifying the effect of age at menarche (analysis of joint effects). The findings are discussed in the context of cohort experiences, examining implications for both early and later-life influences on menopause age.