Association of Historical Redlining With Gestational Diabetes Mellitus: The Mediating Role of BMI and Area Deprivation Index.

Objective: We investigated the association between historic redlining and risk of gestational diabetes mellitus (GDM) and whether this relationship is mediated by maternal obesity and area-level deprivation.

Research design and methods: This retrospective study included 86,834 singleton pregnancies from Kaiser Permanente Southern California's health records (2008-2018). Redlining was assessed using digitized Home Owners' Loan Corporation (HOLC) maps, with patients' residential addresses geocoded and assigned HOLC grades (A, B, C, or D) based on their geographic location within HOLC-graded zones. For GDM case patients, exposure was assigned based on address at diagnosis date; for noncase patients, it was assigned based on address during the 24th to 28th gestational week. Health records were combined with area deprivation index (ADI) from 2011 to 2015 census data. Mixed-effect logistic regression models assessed associations between redlining and GDM, with mediation by BMI and ADI evaluated using inverse odds ratio weighting. Models were adjusted for maternal age, education, race and ethnicity, neighborhood-level income, and smoking status.

Results: Among the 10,134 (11.67%) GDM case patients, we found increased risk of GDM in B ("still desirable," adjusted odds ratio [aOR] 1.20, 95% CI 0.99-1.44), C-graded ("definitely declining," aOR 1.22, 95% CI 1.02-1.47), and D-graded ("hazardous," i.e., redlined, aOR 1.30, 95% CI 1.08-1.57) neighborhoods compared with the "best"-graded zone. Prepregnancy BMI and ADI mediated 44.2% and 64.5% of the increased GDM risk among mothers in redlined areas.

Conclusions: Historic redlining is associated with an increased risk of GDM, mediated by maternal obesity and neighborhood deprivation. Future research is needed to explore the complex pathways linking redlining to pregnancy outcomes.