Abstract
OBJECTIVE: To assess the differences in brain growth between extreme preterm [EP](22-28wks gestation age [GA]) and very preterm infants [VP](28+1-32wks GA) using two-dimensional cranial ultrasound(cUS) at term equivalence. STUDY DESIGN: Retrospective study of neonates born at GA of ≤ 32 weeks between 1st January 2019 and 31st December 2022, without major parenchymal brain injury. RESULTS: 326 neonates, with 207 EP and 119 VP, were enrolled. EP infants compared to VP had significantly lower biparietal diameter [7.7vs7.9 cm, p = 0.003], corpus-callosum length [3.8vs4.1 cm, p < 0.001], corpus-callosum-fastigial distance [4.5vs4.8 cm, p = 0.004] and cerebellar-vermis height [2.1vs2.2 cm, p = 0.002]. Cumulative postnatal steroid exposure had no significant association with brain metrics; however, exposure to antenatal steroids was negatively associated with corpus-callosum length [β = -0.38 (-0.58 to -0.7),p = 0.0003] and pons anteroposterior depth [β = -0.36 (-0.47 to -0.25),p < 0.0001] despite adjustments for clinically important risk factors. CONCLUSION: Preterm infants born ≤ 28 weeks GA have significantly smaller dimensions of major white matter tracts than preterm infants born 28-32 weeks GA at term equivalence. Exposure to antenatal steroids negatively impacts corpus-callosum length and pons anteroposterior depth.