The association of low body mass index with neonatal morbidities in preterm infants

Little is known about the association between body proportionality at birth and neonatal outcomes in preterm infants. Body mass index (BMI) is one of the weigh-for-length ratios that represent body proportionality. The objective of this study was to examine whether BMI at birth affects neonatal outcomes in preterm infants. We assessed 3115 preterm (< 30 weeks), very low birth weight (< 1500 g) infants born between January 2013 and December 2016 and registered in the Korean Neonatal Network database. Using gender-specific BMI for gestational age curves, z-scores of BMI at birth were calculated. Low-, normal-, and high-BMI were defined as BMI z-scores of less than − 1, from − 1 to 1, and greater than 1, respectively. Neonatal morbidities and mortality in low- and high-BMI groups were compared to those in normal-BMI group. The low-BMI group had an increased risk of bronchopulmonary dysplasia, bronchopulmonary dysplasia or death, and necrotizing enterocolitis after adjusting for baseline characteristics and the birth weight z-score. High-BMI group had comparable neonatal outcomes to those of normal-BMI group. Low BMI at birth was associated with an increased risk of bronchopulmonary dysplasia and necrotizing enterocolitis, whereas High BMI at birth was not associated with adverse neonatal outcomes.