Gestational age and 1-year hospital admission or mortality: a nation-wide population-based study

Background: Describe the 1-year hospitalization and in-hospital mortality rates, in infants born after 31 weeks of gestational age (GA). Methods: This nation-wide population-based study used the French medico-administrative database to assess the following outcomes in singleton live-born infants (32-43 weeks) without congenital anomalies (year 2011): neonatal hospitalization (day of life 1 - 28), post-neonatal hospitalization (day of life 29 - 365), and 1-year in-hospital mortality rates. Marginal models and negative binomial regressions were used. Results: The study included 696,698 live-born babies. The neonatal hospitalization rate was 9.8%. Up to 40 weeks, the lower the GA, the higher the hospitalization rate and the greater the likelihood of requiring the highest level of neonatal care (both p < 0.001). The relative risk adjusted for sex and pregnancy-related diseases (aRR) reached 21.1 (95% confidence interval [CI]: 19.2-23.3) at 32 weeks. The post-neonatal hospitalization rate was 12.1%. The raw rates for post-neonatal hospitalization fell significantly from 32 -40 and increased at 43 weeks and this persisted after adjustment (aRR = 3.6 [95% CI: 3.3-3.9] at 32 and 1.5 [95% CI: 1.1-1.9] at 43 compared to 40 weeks). The main causes of post-neonatal hospitalization were bronchiolitis (17.2%), gastroenteritis (10.4%) ENT diseases (5.4%) and accidents (6.2%). The in-hospital mortality rate was 0.85%, with a significant decrease (p < 0.001) according to GA at birth (aRR = 3.8 [95% CI: 2.4-5.8] at 32 and 6.6 [95% CI: 2.1-20.9] at 43, compared to 40 weeks. Conclusion: There's a continuous change in outcome in hospitalized infants born above 31 weeks. Birth at 40 weeks gestation is associated with the lowest 1-year morbidity and mortality.