Outcomes of outborn extremely preterm neonates admitted to a NICU with respiratory distress.

OBJECTIVE: To compare the risk of mortality and morbidity between outborn and propensity score-matched inborn extremely preterm neonates.

SETTING: Multiple neonatal intensive care units (NICU) across the USA.

PATIENTS: Singleton neonates born at 22-29 weeks' gestation with no major anomalies who were admitted to a NICU and discharged between 2000 and 2014. Outborn neonates were restricted to those who transferred into a NICU on the day of birth.

METHODS: The association between inborn-outborn status and the time-to-event outcomes of in-hospital mortality and necrotising enterocolitis (NEC) were assessed using Cox proportional hazards regression. Logistic regression was used to assess the remaining secondary outcomes: retinopathy of prematurity requiring treatment (tROP), chronic lung disease (CLD), periventricular leucomalacia (PVL) and severe intraventricular haemorrhage (IVH). Since outborn status was not random, we used 1:1 propensity score matching to reduce the imbalance in illness severity.

RESULTS: There were 59 942 neonates (7991 outborn) included in the study. Outborn neonates had poorer survival than inborns and higher rates of NEC, severe IVH, tROP and PVL. Inborn-outborn disparities in mortality were reduced over the study period. When analysing the matched cohort (6524 matched pairs), outborns were less likely to die in-hospital compared with inborns (HR 0.84, 95% CI 0.77 to 0.91). However, outborns experienced higher rates of NEC (HR 1.14, 95% CI 1.04 to 1.25), severe IVH (OR 1.52, 95% CI 1.38 to 1.68), tROP (OR 1.45, 95% CI 1.25 to 1.69) and CLD (OR 1.12, 95% CI 1.01 to 1.24).

CONCLUSION: Additional research is needed to understand the contributors to increased morbidity for outborn extremely preterm neonates and identify interventions that mitigate this risk.