Effect of hospital delivery volume and travel time on maternal postpartum health service use in Norway: a nationwide population‑based cohort study

BACKGROUND We investigated the effect of hospital delivery volume and travel time on maternal postpartum health service use in Norway. METHODS We conducted a population-based study including women giving birth from 2008 to 2021. Exposures were (1) annual delivery volume at the observed delivery hospital and travel time by car from the municipality center to the observed delivery hospital, and (2) expected delivery volume and expected travel time based on hospital catchment patterns. The primary outcome was maternal postpartum health service use. We used pseudo–maximum likelihood Poisson regression with adjustment for maternal characteristics, timing of birth, and pre-pregnancy health service use; within-woman analyses used fixed effects. RESULTS The study included 792,330 childbirths by 492,080 women. In the first approach, higher hospital volume (2000 vs. 500 births/year) was associated with 15% more days of GP contacts with a psychiatric diagnosis code (RR 1.15, 95% CI 1.05–1.26). Longer travel time (120-min vs. 30-min) was associated with a 20% longer delivery admission (RR 1.20, 95% CI 1.12–1.28), 5% more days of GP contact (RR 1.05, 95% CI 1.03–1.07), and 10% more days of GP contacts for conversation therapy (RR 1.10, 95% CI 1.01–1.20). In the within-woman analysis, these associations largely disappeared, except for a 13–19% increase in out-of-hours GP contacts at higher volume hospitals. CONCLUSIONS We found little evidence of a causal effect of hospital volume or travel time on overall postpartum health service use. Associations in conventional analyses may reflect residual confounding.