Differential Morbidity in Preterm Small versus Appropriate for Gestational Age: Perhaps Unverifiable.

Objective: The objective of this study was to determine the morbidity of preterm small for gestational age (SGA) infants compared with appropriate for GA (AGA).

Study Design: This is a secondary analysis of the randomized trial evaluating magnesium sulfate for the prevention of cerebral palsy (CP). We compared outcomes of preterm (< 37 weeks) nonanomalous infants who were SGA (birth weight < 10% for GA) versus AGA (birth weight 10-89% for GA). We compared (1) the parent trial primary outcome, a composite of stillbirth, infant death by 1 year of age, or moderate to severe CP at 2 years of age and (2) composite neonatal morbidity (CNM).

Results: Of the 1,948 infants who met inclusion criteria, 95% were AGA and 5% were SGA. The primary outcome was similar (10 and 15%, p = 0.08), as was the CNM (24 and 25%, p = 0.89). Sample size calculations indicate that detection of a one-third higher rate of CNM among SGA compared with AGA infants requires more than 93,900 preterm births; for a one-third difference in moderate to severe CP, more than 1.4 million infants.

Conclusion: Owing to the prohibitive sample size required, ascertaining a difference in sequela between preterm SGA and AGA infants is possibly unverifiable.