Retrospective analysis of leukemoid reactions in extremely preterm infants in a tertiary NICU from 2018-2021

Background: Neonatal leukemoid reaction is associated with higher risk of mortality, chronic lung disease and has been associated with chorioamnionitis. Literature on extremely low birth weight infants with leukemoid reaction is limited. Objectives: The aim of our study was to characterize the maternal and placental factors associated with neonatal leukemoid reaction and to describe outcomes of these ELBW infants. Our objective was to assess if there were maternal factors that would assist the decision-making process regarding the delivery of preterm infants at risk of chorioamnionitis and the sequelae of this inflammatory process. Methods: This was a retrospective case-control study performed in a single, tertiary Maternity Hospital in Dublin. Two matched controls were identified for each case based on gestation and year of birth and data was collected on both the infants and their mothers. Results: 7 extremely preterm neonates were identified as having a leukemoid reaction, defined as a total white cell count of >50,000 or in the first seven days of life. Baseline characteristics between the groups were similar. The median gestational age in the cases group was 24 + 4 weeks and in the control group was 24 + 1. The mean birthweight was 650 g in the cases group vs. 655 g in the control group. There was a higher percentage of males in the control group, 42.9% vs 28.6% in the cases. The preterm infants with leukemoid reaction had a longer duration of ventilation with a median of 18 days (7.5-23.5 days) compared to 6.5 days (2.8-24.5 days) in the control group. More infants in the leukemoid reaction group required inotropes for hypotension in the first 72 h after delivery (42.9% vs 7.1% in the controls, p value .169). Death or Bronchopulmonary dysplasia (BPD) occurred in 85.7% of the cases identified with a leukemoid reaction vs 71.4% of the controls matched. Median maternal CRP was higher in cases prior to delivery vs the controls (66 vs 18.1 mg/L, p-value = .2151). There was histological evidence of maternal inflammatory response in all cases with fetal inflammatory response in 71% of cases. Conclusions: Leukemoid reaction in ELBW infants with evidence of maternal and fetal inflammatory response syndrome on placental histology is associated with a longer duration of initial ventilation, increased need for inotropes in the first 72 h after birth, higher rates of death, and BPD. Prospective studies are required to identify potential biomarkers such as proinflammatory cytokines, IL-6, which might aid the decision-making process in delivery.