Association of reproductive factors and chronic kidney disease in postmenopausal women: results from the U.S. National Health and Nutrition Examination Survey 1999 - 2020.

Chronic kidney disease (CKD) poses a growing global health burden, and reproductive history may influence CKD risk via hormonal pathways. We conducted a population-based cross-sectional analysis using ten cycles of the National Health and Nutrition Examination Survey (NHANES, 1999-March 2020), including 12,912 postmenopausal women with complete reproductive and kidney data. CKD was defined as estimated glomerular filtration rate <60 mL/min/1.73 m2 (CKD Epidemiology Collaboration 2021) or urinary albumin-to-creatinine ratio ≥30 mg/g. Survey-weighted logistic regression and restricted cubic spline models were used to examine associations between reproductive factors and CKD, adjusting for demographic and clinical confounders. After adjustment, higher parity was associated with increased CKD odds: three to four live births (OR = 1.17, 95% CI 1.01-1.34) and five or more live births (OR = 1.22, 95% CI 1.03-1.46) compared with one to two live births. Younger age at first live birth also increased risk (≤20 years: OR = 1.36, 95% CI 1.06-1.75; 21-24 years: OR = 1.35, 95% CI 1.07-1.72). In contrast, hormone replacement therapy (OR = 0.75, 95% CI 0.66-0.84) and oral contraceptive (OR = 0.79, 95% CI 0.69-0.91) use were inversely associated with CKD. Other reproductive factors, including age at menarche, menopause, reproductive span, hysterectomy, bilateral oophorectomy, and type of menopause, showed no significant associations. Restricted cubic spline analyses indicated nonlinear relationships for most continuous reproductive exposures, except age at menarche, which was approximately linear. These findings suggest reproductive history may influence kidney health in postmenopausal women and warrant further studies to clarify underlying mechanisms.