Two denominators for one numerator: the example of neonatal mortality

Area of Science:

• Perinatology
• Neonatal Health
• Epidemiology

Background:

• Preterm delivery is a major predictor of neonatal mortality.
• Neonatal mortality has dual origins: intrauterine pathologies affecting fetuses and immaturity/delivery complications affecting live births.
• Distinguishing direct and indirect effects on neonatal mortality is challenging due to overlapping risk sets.

Purpose of the Study:

• To evaluate the repercussions of using distinct denominators (fetuses vs. live births) for neonatal mortality risk assessment.
• To determine if gestational age conditioning can adequately account for the mediating effect of preterm birth.
• To assess the meaningfulness of gestational-age-specific neonatal mortality definitions.

Main Methods:

• Simulations were used to model neonatal mortality with separate fetal and neonatal risk factors.
• An exposure was introduced that increased preterm birth risk without altering baseline mortality risks.
• Apparent gestational-age-specific mortality was calculated using both fetal and live birth denominators for exposed and unexposed groups.

Main Results:

• Apparent exposure effects on neonatal mortality were observed regardless of the denominator used (fetuses or live births).
• Conditioning on gestational age did not fully block the mediating effect of preterm delivery.
• Neither denominator provided a statistically meaningful definition of gestational-age-specific neonatal mortality, except for predictive purposes.

Conclusions:

• The dual risk set structure complicates accurate assessment of neonatal mortality.
• Current methods using either fetal or live birth denominators are insufficient for defining meaningful gestational-age-specific neonatal mortality.
• Further research is needed to refine methodologies for understanding neonatal mortality risk factors and their impact.