Reproductive history and age at natural menopause in US women: a cross-sectional analysis of National Health and Nutrition Examination Survey 1999 to March 2020

Objective: The associations of parity and gravidity with age at natural menopause (ANM) remain incompletely characterized. We examined parity‐ANM and gravidity‐ANM associations and explored non‐live-birth pregnancies descriptively in a nationally representative sample of US women. Methods: This cross-sectional analysis used National Health and Nutrition Examination Survey 1999 to March 2020 data and included women with confirmed natural menopause and ANM restricted to 30 to 59 years. Survey-weighted linear regression with multiple imputation estimated mean differences in ANM for parity and gravidity. Model 2, adjusted for demographic, socioeconomic, and behavioral factors, was prespecified as the primary model. Benjamini‐Hochberg false discovery rate correction was applied separately to main associations, nonlinearity, and interactions. Restricted cubic splines assessed nonlinearity. Results: The analytic samples included 7,047 women for parity models and 7,058 for gravidity models. In the primary model, gravidity of 3 to 4 versus 0 was associated with 0.62 years later ANM (95% CI: 0.02 to 1.23; nominal P = 0.043), but this association did not remain significant after false discovery rate correction (q = 0.17). No categorical or continuous contrast for parity or gravidity was significant after correction. Apparent nonlinearity in minimally adjusted models was attenuated after covariate adjustment (nonlinearity q = 0.16 for both parity and gravidity). The derived non‐live-birth-pregnancy measure showed no stable descriptive pattern, and no prespecified interaction was significant. Conclusion: Higher gravidity showed a small, nonconfirmatory association with later ANM at moderate exposure levels. The findings do not support a robust nonlinear relationship or a simple cumulative ovulation-sparing model.