Seasonality, Weather, and Obstetric Level of Care: An Analysis of Rural Delivery Locations.

Birth seasonality in the United States typically peaks in late summer, yet research has rarely examined these patterns in northern mountainous regions or across different hospital obstetric levels. This study investigates the temporal dynamics of maternal healthcare-seeking behavior in Montana, specifically focusing on seasonality in birth volume and obstetric bypassing (delivering at a non-local hospital). We conducted a retrospective analysis of 98,524 birth records (2014-2022) at hospitals with Level 1, 2, and 3 obstetric units, integrating driving distances and monthly county-level climate data. Statistical analyses included calculating observed-to-expected (O-E) ratios to identify seasonality and regression models to test interactions between season, hospital level, and weather. Montana birth volume is distinguished by a peak in June and a trough in January, with seasonality most pronounced at Level 3 hospitals. Obstetric bypassing significantly decreases during winter (O-E ratio 0.95), particularly for Level 1 hospitals, while increasing during warm, high-precipitation months. Over time, bypassing toward Level 3 hospitals has risen from 13.6% to 20%. We conclude that seasonality and weather correlates are associated with significant variation in care-seeking patterns, reflecting the unique challenges facing rural hospitals.