Factors Associated with Diagnosis-Based Incident Mild Cognitive Impairment in Middle-Aged Women: A 14-Year National Cohort Study

Background/Objectives: This study aimed to identify sociodemographic, physiological, lifestyle-related, reproductive, and comorbidity factors associated with diagnosis-based incident mild cognitive impairment (MCI) among middle-aged Korean women and to descriptively compare findings from complete-case analysis (CCA) with results from five separately imputed datasets. Methods: This retrospective cohort study used customized data from the Korean National Health Insurance Service from 2009 to 2022. The source population comprised women aged 40–65 years who underwent general and cancer health screenings during 2009–2010. After eligibility and disease-related exclusions and removal of duplicate records, 2,178,195 women remained before missing-data handling. CCA included 483,184 women, of whom 34,976 met the definition of diagnosis-based incident MCI during 2011–2022. Diagnosis-based incident MCI was operationally defined as Korean Standard Classification of Diseases code F06.7 recorded as the primary or first secondary diagnosis on at least two separate healthcare dates. Five imputed datasets were generated from the dataset before listwise deletion and analyzed separately without Rubin’s-rule pooling. Multivariable logistic regression was used to examine associated factors. Longitudinal-change variables compared measurements from 2009–2010 and 2021–2022 and were interpreted as associated factors rather than temporally established predictors. Results: In the CCA, associations with diagnosis-based incident MCI were observed for age, changes in employment status, BMI, physical activity, selected reproductive characteristics, and several comorbidities. Results from the five separately imputed datasets showed somewhat different patterns for several socioeconomic, physiological, lifestyle-related, reproductive, and comorbidity factors. Because the five imputed datasets were analyzed separately without Rubin’s-rule pooling, these findings were interpreted descriptively rather than as pooled multiple-imputation estimates. An exploratory sensitivity analysis using a broader composite cognitive and neurological outcome showed generally similar directions and magnitudes for several major associations. Conclusions: Diagnosis-based incident MCI in middle-aged women was associated with multidimensional health characteristics, including reproductive and comorbidity-related factors. However, differences between the CCA and results from the five separately imputed datasets cannot be attributed solely to missing-data handling and should be interpreted in light of differences in analytic procedures, temporal limitations, and substantial missingness.