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Outcomes of outborn extremely preterm neonates admitted to a NICU with respiratory distress
  1. Jennifer L Fang1,
  2. Kristin C Mara2,
  3. Amy L Weaver2,
  4. Reese H Clark3,
  5. William A Carey1
  1. 1 Division of Neonatal Medicine, Mayo Clinic, Rochester, Minnesota, USA
  2. 2 Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, Minnesota, USA
  3. 3 CREQS, Pediatrix Medical Group, Sunrise, Florida, USA
  1. Correspondence to Dr Jennifer L Fang, Neonatal Medicine, Mayo Clinic, Rochester MN 55905, USA; fang.jennifer{at}


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.

  • neonate
  • prematurity
  • respiratory distress syndrome

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  • Contributors JF conceptualised and designed the study, interpreted the data and drafted the manuscript. KCM and AW designed and conducted the statistical analyses, interpreted the data and drafted the manuscript. RHC conceptualised the study, acquired the data, interpreted the data and critically reviewed and revised the manuscript. WC conceptualised and designed the study, interpreted the data and revised the manuscript. All authors approved the final manuscript as submitted.

  • Funding Data analysis was funded by the Mayo Clinic Children’s Research Center.

  • Competing interests None declared.

  • Ethics approval The Mayo Clinic Institutional Review Board (IRB; Rochester, MN) deemed this study exempt. The Western IRB approved the use of this data set for the study.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Correction notice This paper has been amended since it was published Online First. There was a grammatical error inserted during the production stage and this has now been corrected. We have also added the authors' middle initials to the author names.

  • Patient consent for publication Not required.