Neonatal and postneonatal mortality: useful constructs or outdated concepts?

Area of Science:

• Pediatrics
• Public Health
• Epidemiology

Background:

• Infant deaths are historically categorized as neonatal (first 28 days) or postneonatal (28 days to 1 year).
• Neonatal deaths were typically endogenous (perinatal, biologic), while postneonatal deaths were exogenous (nonperinatal, injuries, socioenvironmental).
• This traditional dichotomy is being re-evaluated due to evolving causes of infant mortality.

Purpose of the Study:

• To examine the congruence between the traditional neonatal-endogenous and postneonatal-exogenous infant death classifications.
• To assess the continued utility of the neonatal-postneonatal age-based categorization for infant mortality analysis.
• To explore alternative methods for classifying infant deaths.

Main Methods:

• Analysis of underlying cause of death data for Wisconsin resident birth cohorts from 1979 to 1986.
• Comparison of infant mortality rates by cause of death within neonatal and postneonatal periods.
• Evaluation of birth weight-specific mortality rates across different causes and age categories.

Main Results:

• Birth weight-specific neonatal and postneonatal mortality rates remained stable during the 1980s.
• Significant differences in the distribution of endogenous and exogenous causes of death between neonatal and postneonatal periods were observed.
• Neonatal mortality largely aligns with endogenous causes, but postneonatal mortality is no longer exclusively exogenous.

Conclusions:

• The traditional neonatal-postneonatal classification is an increasingly unreliable proxy for distinguishing endogenous and exogenous infant deaths.
• Postneonatal deaths are not solely attributable to exogenous factors, challenging the historical classification.
• Alternative infant death classification methods, such as corrected gestational age or in-hospital mortality rates, warrant further investigation.