Association of outborn versus inborn birth status on the in-hospital outcomes of neonates treated with therapeutic hypothermia: A propensity score-weighted cohort study

Objective: To compare the risk of in-hospital mortality and morbidity between outborn and inborn neonates treated with whole body hypothermia.

Methods: The association of outborn birth status with in-hospital mortality and morbidity, prior to NICU discharge or transfer, was assessed in a large historical cohort of neonates who had therapeutic hypothermia initiated on the day of birth. The cohort was restricted to neonates born at ≥35 weeks gestational age from 2007 to 2018. Since the sample was non-random, inverse probability weighting (IPW) derived from propensity scores was used to reduce imbalance in baseline maternal and neonatal characteristics between outborn and inborn neonates. Cox proportional hazards regression was used to assess the association between outborn status and in-hospital mortality.

Results: There were 4447 neonates included in the study (2463 outborn). Outborn status was not significantly associated with an increased risk of in-hospital mortality in the unadjusted cohort (HR = 1.17, 95% CI 0.97-1.42, p = 0.10) or IPW cohort (HR = 1.09, 95% CI 0.95-1.26, p = 0.22). However, in the IPW cohort, outborn neonates were significantly more likely to have seizures (28% vs 24%, p = 0.006), anticonvulsant exposure (46% vs 41%, p = 0.002), and gastrostomy tube placement (5.8% vs 3.8%, p = 0.009) during their newborn hospitalization.

Conclusion: Outborn status was not significantly associated with increased in-hospital mortality among neonates treated with whole body hypothermia. However, outborn neonates were more likely to have seizures, receive anticonvulsant treatment, and undergo gastrostomy tube placement. Further study is needed to better understand the etiologies of these outcome disparities and potential implications for long-term neurodevelopmental outcomes.