Mortality and morbidity risks vary with birth weight standard deviation score in growth restricted extremely preterm infants

•Mortality and morbidity risks in growth restricted extremely preterm infants•A multicenter retrospective cohort study in Japan•Cut-off points to predict adverse outcomes vary with birth weight standard deviation.

ObjectiveTo assess whether the mortality and morbidity risks vary with birth weight standard deviation score (BWSDS) in growth restricted extremely preterm infants.Study designThis was a multicenter retrospective cohort study using the database of the Neonatal Research Network of Japan and including 9149 infants born between 2003 and 2010 at < 28 weeks gestation. According to the BWSDSs, the infants were classified as: <− 2.0, − 2.0 to − 1.5, − 1.5 to − 1.0, − 1.0 to − 0.5, and  ≥ − 0.5. Infants with BWSDS ≥ − 0.5 were defined as non-growth restricted group.ResultsAfter adjusting for covariates, the risks of mortality and some morbidities were different among the BWSDS groups. Compared with non-growth restricted group, the adjusted odds ratio (aOR) for mortality [aOR, 1.69; 95% confidence interval (CI), 1.35–2.12] and chronic lung disease (CLD) (aOR, 1.28; 95% CI, 1.07–1.54) were higher among the infants with BWSDS − 1.5 to <− 1.0. The aOR for severe retinopathy of prematurity (ROP) (aOR, 1.36; 95% CI, 1.09–1.71) and sepsis (aOR, 1.72; 95% CI, 1.32–2.24) were higher among the infants with BWSDS − 2.0 to <− 1.5. The aOR for necrotizing enterocolitis (NEC) (aOR, 2.41; 95% CI, 1.64–3.55) was increased at a BWSDS < − 2.0.ConclusionBeing growth restricted extremely preterm infants confer additional risks for mortality and morbidities such as CLD, ROP, sepsis and NEC, and these risks may vary with BWSDS.