Relationship between neonatal nucleated red blood cell counts and hypoxic-ischemic injury

To determine if nucleated red blood cell counts(RBC) are different in infants who develop intraventricular hemorrhage and periventricular leukomalacia in the first week of life and in those who do not.

Nucleated RBCs were obtained from 441 infants weighing more than 499 g and less than 1751 g. Neonatal cranial fontanel sonography was performed on days 3 and 7 of life, and neonates were divided into those with normal and abnormal sonographic findings. The nucleated RBCs were compared between these groups and between normal and abnormal groups matched for birth weight and gestational age.

Mean gestational age, birth weight, birth weight percentile, Apgar score, respiratory distress syndrome and mortality were different between the infants with normal and abnormal ultrasound findings. The nucleated RBCs (per 100 white blood cells) were not different (40.5 +/- 126.8 versus 41.8 +/- 71.7, t = 0.09, P = .9). When we controlled for gestational age and birth weight, there was no significant difference between nucleated RBCs in those with normal and abnormal sonography (54.3 +/- 206.5 versus 41.4 +/- 72.0,t = 0.56, P = .6). In growth-restricted neonates, there was a significant increase in nucleated RBCs regardless of whether growth restriction was defined as tenth percentile or less, 25th percentile or less, or 50th percentile or less, even when we controlled for gestational age.

Nucleated RBCs are not different in preterm infants with or without intraventricular hemorrhage and periventricular leukomalacia, even when one controls for gestational age and birth weight. There are significant elevations in nucleated RBCs in growth-restricted fetuses. Birth weight percentile must be considered when using nucleated RBCs as a marker of intrauterine hypoxia.