Early Reproductive Experience and Risk of Kidney Function Decline in Middle-aged and Older Chinese Women: A Cohort Study

Introduction: Chronic kidney disease (CKD) affects approximately 850 million people worldwide, and the CKD prevalence in Chinese adults is approximately 10.8%. Women undergo unique physiological changes during pregnancy, with glomerular filtration rate increasing by 40%-50%. However, evidence regarding the association between basic reproductive factors and kidney function remains limited, particularly in Chinese populations. Methods: Using data from the China Health and Retirement Longitudinal Study (CHARLS) 2011 baseline and 2015 follow-up, we included 4,180 female participants with serum creatinine measurements (3,057 with cystatin C data for combined eGFR calculation). Exposure variables were parity (≤2 vs >2 children) and age at first birth (AFB) (<20, 20-25, >25 years). Outcomes included estimated glomerular filtration rate (eGFR), incident CKD, and rapid kidney function decline. Multivariable linear and logistic regression models with stepwise covariate adjustment were applied. Results: The mean age was 57.3 ± 9.2 years; 67.7% were postmenopausal. In the fully adjusted model, women with parity >2 had 1.98 mL/min/1.73m² lower baseline eGFR (95%CI: -3.43 to -0.54, P=0.007) and 1.74 mL/min/1.73m² lower mean eGFR (95%CI: -3.04 to -0.45, P=0.008) compared with parity ≤2. Women with AFB >25 years had 74% lower risk of incident CKD (OR=0.26, 95%CI: 0.08-0.83, P=0.023) compared with AFB <20 years. Subgroup analysis in postmenopausal women showed consistent results. Conclusions: Higher parity was independently associated with lower kidney function levels, while older AFB was associated with lower risk of incident CKD. Reproductive history may serve as a reference indicator for kidney function assessment in middle-aged and older women.