Association Between Birth Timing and Early Clinical Outcomes in Very Preterm Infants: A Retrospective Cohort Study

Background: The effect of birth timing on outcomes in very preterm infants remains controversial. This study evaluated the association between birth timing and early morbidity and mortality in infants born before 32 weeks of gestation. Methods: In this retrospective single-center cohort study, inborn infants born at <32 weeks’ gestation between January 2021 and May 2023 were categorized as in-hours (weekdays 08:01–16:00) or out-of-hours (weekdays 16:01–08:00, weekends, official holidays). The primary outcome was a composite of early mortality (≤72 h) or severe intraventricular hemorrhage (grades III–IV). Multivariable logistic regression adjusted for baseline confounders (Model 1); delivery-room resuscitation, a potential mediator, was added in Model 2. Results: Of 363 infants, 160 (44.1%) were born in-hours and 203 (55.9%) out-of-hours. The composite outcome occurred in 19.7% versus 12.5% (p = 0.091; Model 1 aOR 1.46, 95% CI 0.77–2.77). Overall mortality (32.5% vs. 21.3%, p = 0.023), early mortality (8.4% vs. 2.5%, p = 0.022), delivery-room resuscitation (56.7% vs. 36.9%, p < 0.001), and respiratory distress syndrome (69.0% vs. 55.6%, p = 0.012) were higher out-of-hours. Out-of-hours birth was associated with higher mortality in Model 1 (aOR 1.88, 95% CI 1.11–3.20), but the estimate was attenuated and imprecise in Model 2 (aOR 1.58, 95% CI 0.91–2.75). Conclusions: Out-of-hours birth was not significantly associated with the composite primary outcome but was associated with higher crude and baseline-adjusted mortality. Because delivery urgency, illness severity, and staffing at delivery were incompletely measured, residual confounding cannot be excluded.