The association of cerebral palsy and death with small-for-gestational-age birthweight in preterm neonates by individualized and population-based percentiles

Objective The objective of the study was to determine whether an individualized growth standard (IS) improves the identification of preterm small-for-gestational-age (SGA) neonates at risk of developing moderate/severe cerebral palsy (CP) or death. Study Design This study was a secondary analysis of data from a randomized trial of MgSO₄ for the prevention of CP or death among anticipated preterm births. Singleton nonanomalous liveborns delivered before 34 weeks' were classified as SGA (less than the 10th percentile for their gestational age) by a population standard (PS) or an IS (incorporating maternal age, height, weight, parity, race/ethnicity, and neonatal sex). The primary outcome was the prediction of moderate or severe CP or death by age 2 years. Results Of 1588 eligible newborns, 143 (9.4%) experienced CP (n = 33) or death (n = 110). Forty-four (2.8%) were SGA by the PS and 364 (22.9%) by the IS. All PS-SGA newborns also were identified as IS-SGA. SGA newborns by either standard had a similarly increased risk of CP or death (PS: relative risk [RR], 2.4, 95% confidence interval [CI], 1.3-4.3 vs IS: RR, 1.8, 95% CI, 1.3-2.5, respectively). The similarity of RRs remained after stratification by the MgSO₄ treatment group. The IS was more sensitive (36% vs 6%, P <.001) but less specific (78% vs 98%, P <.001) for CP or death. The receiver operating characteristic curve analysis revealed a statistically lower area under the curve for the PS, although the ability of either method to predict which neonates would subsequently develop CP or death was poor (PS: 0.55, 95% CI, 0.49-0.60 vs IS: 0.59, 95% CI, 0.54-0.64, P <.001). Conclusion An individualized SGA growth standard does not improve the association with, or prediction of, CP or death by age 2 years.