Title: Maternal complications after cesarean section by obstetric facility type in Japan: A claims-based cohort study

Aim: Little is known about patient safety in a less consolidated obstetric system where various facilities, such as perinatal medical centers (PMCs), general hospitals, and clinics, collaborate under risk-based role differentiation. We aimed to compare maternal complications after cesarean section by facility type across area types (rural, provincial, and metropolitan) in Hokkaido, Japan. Methods: This retrospective cohort study used insurance claims data from Hokkaido (2018-2025). Two comparisons were conducted for a composite outcome of postpartum hemorrhage, infection, and thrombosis: a two-category comparison (PMC vs. non-PMC, combining general hospitals and clinics) across all areas, with an interaction term between facility and area type; a three-category comparison (PMC vs. general hospital vs. clinic) restricted to metropolitan areas. Generalized estimating equations with a Poisson distribution, accounting for clustering within facilities, were applied to estimate risk ratios. Results: A total of 1,822 participants underwent cesarean section. PMCs were associated with lower maternal complication rates compared to non-PMC facilities (adjusted RR 0.37, 95% CI 0.16-0.88 in rural areas; adjusted RR 0.20, 95% CI 0.11-0.37 in provincial areas). In metropolitan areas, PMCs and general hospitals were associated with lower maternal complication rates compared to clinics (PMC vs clinic: adjusted RR 0.42, 95% CI 0.18-0.97; general hospital vs clinic: adjusted RR 0.25, 95% CI 0.09-0.70). Conclusions: Higher-level facilities were associated with lower maternal complication rates after cesarean section in Japan. These findings provide important evidence for regional consolidation of obstetric care.