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Understanding the relative contributions of prematurity and congenital anomalies to neonatal mortality



To examine the relative contributions of preterm delivery and congenital anomalies to neonatal mortality.

Study design

Retrospective analysis of 2009–2011 linked birth cohort-hospital discharge files for California, Missouri, Pennsylvania and South Carolina. Deaths were classified by gestational age and three definitions of congenital anomaly: any ICD-9 code for an anomaly, any anomaly with a significant mortality risk, and anomalies recorded on the death certificate.


In total, 59% of the deaths had an ICD-9 code for an anomaly, only 43% had a potentially fatal anomaly, and only 34% had a death certificate anomaly. Preterm infants (<37 weeks GA) accounted for 80% of deaths; those preterm infants without a potentially fatal anomaly diagnosis comprised 53% of all neonatal deaths. The share of preterm deaths with a potentially fatal anomaly decreases with GA.


Congenital anomalies are responsible for about 40% of neonatal deaths while preterm without anomalies are responsible for over 50%.

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Partial support by the March of Dimes Prematurity Research Center at Stanford University School of Medicine (to CSP and SKS); the Eunice Kennedy Shriver National Institute of Child Health and Human Development (RO1 HD084819 [to CSP, MP, SKS, and SAL].

Author information

Authors and Affiliations



CSP and SAL were co-PIs for the grant that provided funding, conceived of the idea for this study, designed the analysis, supervised the data analysis, interpreted the results, contributed to the framing of the manuscript, and contributed to the revisions to the manuscript. CSP drafted the initial version of the manuscript. MP and SKS were the analysts that actually created the study datasets and conducted the analyses. They provided critical input into the design of the analyses and contributed to the revisions of the manuscript. JAR helped refine the analysis plan and the interpretation of the results, and contributed to the framing of the manuscript and revisions of the manuscript. All authors approved the final version of the manuscript before it was submitted.

Corresponding author

Correspondence to Ciaran S. Phibbs.

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The authors declare no competing interests.

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Supplementary information


Appendix Table A-1: Definitions of the Categories of Congenital Anomalies with a Significant Association with Neonatal Mortality

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Phibbs, C.S., Passarella, M., Schmitt, S.K. et al. Understanding the relative contributions of prematurity and congenital anomalies to neonatal mortality. J Perinatol 42, 569–573 (2022).

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