( BJOG . 2023;130(13):1602–1609. doi: 10.1111/1471-0528.17533) The condition known as neonatal hypoxic ischemic encephalopathy (HIE) occurs when a term or near-term infant suffers asphyxiation during or near birth. The resulting signs and symptoms vary and may be classified as mild, moderate, or severe. Historically, infants diagnosed with mild HIE received alternative, and less intensive care given the understanding that outcomes were less severe compared with infants with the moderate or severe HIE diagnosis. However, recent studies have suggested young children (aged 2 to 5) who were diagnosed with mild HIE as infants are more likely to have a disability when compared with similar aged children without an HIE diagnosis. In addition, when examining mild HIE patients at neonatal discharge, abnormal results were found on amplitude-integrated electroencephalography, brain magnetic resonance imaging, and neurological exam. This population-based cohort study used register-based data to further understand how mild HIE relates to severe neurological outcomes, including death up to 6 years after birth.

Objective: To investigate whether mild neonatal hypoxic ischaemic encephalopathy (HIE) in term born infants is associated with cerebral palsy, epilepsy, mental retardation and death up to 6 years of age.Design: Population-based cohort study.Setting: Sweden, 2009-2015.Population: Live term born infants without congenital malformations or chromosomal abnormalities (n = 505 075).Methods: Birth and health data were retrieved from Swedish national health and quality registers. Mild HIE was identified by diagnosis in either the Swedish Medical Birth Register or the Swedish Neonatal Quality Register. Cox proportional hazards regression was used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs).Main outcome measures: A composite of the outcomes cerebral palsy, epilepsy, mental retardation and death up to 6 years of age.Results: Median follow-up time was 3.3 years after birth. Of 414 infants diagnosed with mild HIE, 17 were classified according to the composite outcome and incidence rates were 12.6 and 2.9 per 1000 child-years in infants with and without HIE respectively. Infants with mild HIE was four times as likely to be diagnosed with the composite outcome (HR 4.42, 95% CI 2.75-7.12) compared with infants without HIE. When analysed separately, associations were found with cerebral palsy (HR 21.50, 95% CI 9.59-48.19) and death (HR 19.10, 95% CI 7.90-46.21). HRs remained essentially unchanged after adjustment for covariates.Conclusions: Mild neonatal HIE was associated with neurological morbidity and mortality in childhood. Challenges include identifying infants who may develop morbidity and how to prevent adverse outcomes.