Supplementary Material for: Association between Infant Birth Size Classification and Development of Morbidities in the Neonatal Intensive Care Unit (NICU): A Cohort Study

Introduction: Morbidities of prematurity are often analyzed as if their epidemiology is shared, but this assumption may mask key differences in morbidity risk. This study assesses the association between three birth size metrics and development of chronic lung disease (CLD), severe retinopathy of prematurity (sROP), severe intraventricular hemorrhage (sIVH), and severe necrotizing enterocolitis (sNEC) when stratified by gestational age (GA) with morbidity-specific GA ranges and covariates.
Methods: For each morbidity, data from the Pediatrix Clinical Data Warehouse (2013-2018) were included for GAs with at least 1% morbidity. Birth weight, length, and head circumference were classified as small (SGA), appropriate (AGA), or large for GA (LGA) using the Olsen curves. Odds ratios and 95% confidence intervals (AGA as referent) for each morbidity by GA were calculated using logistic regression, adjusting for morbidity-specific adjustors.
Results: SGA weight increased the odds of CLD (OR: 1.6-2.9) and sROP (OR: 1.7-3.6) for most GAs and sNEC (OR: 1.6-1.8) in at least half of the GAs, but not sIVH at any GA. LGA weight decreased the odds of CLD in some GAs and increased the odds of sIVH only at 27 weeks GA, but was not associated with sROP or sNEC at any GA. Results were similar for length and head circumference.
Conclusion: CLD, sROP, sNEC, and sIVH are associated with GA, birth size, and covariates differently. CLD and sROP were consistently associated with size classification and GA, while sNEC demonstrated variability in its association. However, sIVH was rarely associated with birth size in this sample.