RESUMO
OBJECTIVES: To quantify the independent risks of neonatal (0-28 days), postneonatal (29-364 days), 1- to 5- and 6- to 30-year mortality by gestational age and investigate changes in survival over time in an Australian birth cohort. STUDY DESIGN: Maternal and birth related Western Australian population data (1980-2010) were linked to the state mortality data using a retrospective cohort study design involving 722 399 live-born singletons infants. RESULTS: When compared with 39- to 41-week born infants, the adjusted risk ratio for neonatal mortality was 124.8 (95% CI 102.9-151.3) for 24-31 weeks of gestation, 3.4 (95% CI 2.4-4.7) for 35-36 weeks of gestation, and 1.4 (95% CI 1.1-1.8) for 37-38 weeks of gestation. For 24-31 weeks of gestation infants, the adjusted hazard ratio for postneonatal mortality (29-364 days) was 13.9 (95% CI 10.9-17.6), for 1- to 5-year mortality 1.4 (95% CI 0.7-3.0) and for 6- to 30-year mortality 1.3 (95% CI 0.8-2.3). The risk of neonatal and postneonatal mortality for those born preterm decreased over time. CONCLUSIONS: In Western Australia, late preterm and early term infants experienced higher risk of neonatal and postneonatal mortality when compared with their full-term peers. There was insufficient evidence to show that gestational length was independently associated with mortality beyond 1 year of age. Neonatal and postneonatal mortality improved with each decade of the study period.