To investigate associations between nucleated red blood cell (NRBC) count in neonates with hypoxic-ischemic encephalopathy (HIE), acute perinatal sentinel events, and neurodevelopmental outcomes and to examine the mechanism(s) causing elevated counts.

We included newborn infants with HIE treated with therapeutic hypothermia with ≥3 NRBC counts during their neonatal intensive care unit hospitalization and neurodevelopmental evaluations at a mean of 24 ± 6 months.

Ninety-five of 152 infants who met our study criteria (63%) had a normal NRBC count after birth, defined as ≤95th percentile of the upper reference interval, and the other 57 (37%) had an elevated count. Documented sentinel events during labor resulting in emergency delivery (eg, acute abruption) (n = 79) were associated with a normal NRBC count (OR, 257; 95% CI, 33-1988). Of the 152 infants evaluated, 134 (88%) survived to discharge. The odds of surviving were 3-fold greater (OR, 3.0; 95% CI, 1.1-8.3) when the first NRBC count was normal than when it was elevated. Normal counts were moderately predictive of infants without neurodevelopmental impairment at a 2-year evaluation (P < .001). NRBC half-life was longer in infants with an elevated NRBC count compared with those with a normal count (60 hours vs 39 hours; P < .01).

In infants with HIE, a normal NRBC count after birth was associated with acute intrapartum events necessitating emergent delivery. Normal counts were modestly predictive of a better prognosis. We speculate that the elevated NRBC counts at birth resulted from hypoxia that occurred earlier or chronically. Impaired clearance of NRBCs from the blood might be one mechanistic explanation for the high counts.