Objectives (1) To operationalise our previously published definition of neonatal serious illness by applying it to a patient cohort and (2) to evaluate timing of palliative care consultation, goals of care discussions and meeting serious illness criteria.

Methods This was a retrospective chart review. Inborn neonates delivered between January 2006 and December 2020 who died prior to neonatal intensive care unit discharge were identified through EPIC query. Kruskal-Wallis and Mann-Whitney-U tests were used to compare time intervals relating to transition to serious illness across causes of death and other factors. χ² tests were used to examine frequency of goals of care conversations by factors.

Results Eighty-eight per cent of patients met criteria for neonatal serious illness within 48 hours of life. There were no significant differences in transition to serious illness between preterm and term infants. Time to identification of serious illness varied significantly by cause of death. Palliative care was consulted for 5.7% of patients.

Conclusion All patients met criteria for serious illness early in life based on our definition. This definition may be useful for identifying neonates with serious illness in time to provide support. Additional work is needed to apply this definition prospectively to explore its utility for clinical care and research.