Eosinophil count trends during the neonatal period in infants born at 22–24 weeks of gestation compared with infants born at 25–28 weeks: A retrospective longitudinal cohort study

Eosinophilia is frequently observed in preterm infants. However, little is known about trends in eosinophil counts in periviable infants. This study aimed to describe eosinophil count trends in infants born at 22-24 weeks of gestation during the neonatal period compared with infants born at 25-28 weeks of gestation. This single-center retrospective cohort study included neonates born between 22 + 0 and 28 + 6 weeks of gestation without congenital anomalies from 2013 to 2022 at our hospital. We described eosinophil count trends in infants born at 22-24 weeks of gestation from birth to 12 weeks of age and compared the trend with those of infants born at 25-28 weeks of gestation. Multiple regression analysis was performed to determine the peak eosinophil counts and potential confounders. A total of 124 infants were analyzed. Eosinophilia (≥700 eosinophils/mm3) was observed in 41/42 (97.6 %) infants born at 22-24 weeks of gestation. Eosinophil counts peaked when the infants were 3-4 weeks of age; this trend did not differ from that in infants born at 25-28 weeks of gestation. Peak eosinophil counts were significantly higher in infants born at 22-24 weeks of gestation. Gestational age and birth weight were negatively associated with peak eosinophil counts (Spearman's rank correlation coefficient [r] = -0.23; p = 0.011 and r = -0.30; p < 0.001, respectively). Clinical parameters were not associated with peak eosinophil counts in infants born at 22-24 weeks of gestation after adjusting for gestational age and birth weight. A significantly higher proportion of infants born at 22-24 weeks of gestation exhibited eosinophilia compared to infants born at 25-28 weeks of gestation; however, both groups of infants had similar peak eosinophilia timing. These results will prompt further studies exploring eosinophilia of prematurity mechanism in this population.