Nucleated red blood cells in preterm infants with retinopathy of prematurity

Objective. The aim of this retrospective study was to examine hematologic indices of potential intrauterine hypoxia, including circulating nucleated red blood cells, lymphocytes, and platelets in preterm infants who developed retinopathy of prematurity (ROP) compared with suitable controls. We hypothesized that higher neonatal absolute nucleated red blood cell (ANRBC) and lymphocyte counts and lower platelets would be found in infants who developed ROP, compared with control infants. Methods. Each of 23 infants with ROP was pair matched for gestational age and Apgar scores with a control without ROP. Criteria for exclusion in both groups included factors that may influence the ANRBCs at birth. Venous ANRBC counts were obtained within 1 hour of life. Statistical analyses used paired t tests, a paired Wilcoxon test, and backward stepwise-regression analysis. Results. Groups did not differ in birth weight, gestational age, Apgar scores, or hematocrit, white blood cell, or platelets counts. The ANRBC counts at birth were significantly higher in infants who developed ROP than in controls. Conclusions. Infants who develop ROP have higher ANRBC counts at birth than matched controls. We suggest that increased fetal erythropoiesis exists in preterm infants who later on will develop ROP. If correct, our interpretation supports the theory that long-lasting fetal hypoxia and/or ischemia may play a role in the pathogenesis of ROP.