Association of gestational age at birth with reasons for subsequent hospitalisation: 18 Years of follow-up in a Western Australian population study

Background: Preterm infants are at a higher risk of hospitalisation following discharge from the hospital after birth. The reasons for rehospitalisation and the association with gestational age are not well understood. Methods: This was a retrospective birth cohort study of all live, singleton infants born in Western Australia between 1^st January 1980 and 31^st December 2010, followed to 18 years of age. Risks of rehospitalisation following birth discharge by principal diagnoses were compared for gestational age categories (<32, 32-33, 34-36, 37-38 weeks) and term births (39-41weeks). Causes of hospitalisations at various gestational age categories were identified using ICD-based discharge diagnostic codes. Results: Risk of rehospitalisation was inversely correlated with gestational age. Growth-related concerns were the main causes for rehospitalisation in the neonatal period (<1 month of age) for all gestational ages. Infection was the most common reason for hospitalisation from 29 days to 1 year of age, and up to 5 years of age. Injury-related hospitalisations increased in prevalence from 5 years to 18 years of age. Risk of rehospitalisation was higher for all preterm infants for most causes. Conclusions: The highest risks of rehospitalisation were for infection related causes for most GA categories. Compared with full term born infants, those born at shorter GA remain vulnerable to subsequent hospitalisation for a variety of causes up until 18 years of age.