Neonatal nucleated red blood cell counts in growth-restricted fetuses: Relationship to arterial and venous Doppler studies

OBJECTIVE: Elevated nucleated red blood cell count in neonatal blood and Do ppler-detected circulatory decompensation in fetuses with intrauterine grow th restriction are associated with hypoxemia. We sought to determine the re lationship between the nucleated red blood cell count at birth and the circ ulatory status of fetuses with intrauterine growth restriction. STUDY DESIGN: Eighty-four fetuses with elevated umbilical artery pulsatilit y index values >2 SD above the gestational age mean and a subsequent birth weight <10th percentile were examined serially Umbilical and middle cerebra l artery pulsatility index, inferior vena cava and ductus venosus peak velo city index, and flow pattern in the umbilical vein (umbilical vein constant vs pulsatile) were recorded. Fetuses were grouped as follows, on the basis of the last examination before delivery: 1, elevated umbilical artery puls atility index only; 2, middle cerebral artery pulsatility index >2 SD below the gestational age mean in addition to abnormal umbilical artery pulsatil ity index; 3, either peak velocity index >2 SD above the gestational age me an in the inferior vena cava and ductus venosus or pulsatile flow in the um bilical vein, or both. Nucleated red blood cells per 100 white blood cells were ascertained in a peripheral blood sample obtained within 1 hour of del ivery with daily follow-up samples until the nucleated red blood cell count was <5/100 white blood cells. RESULTS: Groups 2 (median 38.5, range 1-273) and 3 (median 145, range 2-318 0) had higher nucleated red blood cell counts than group 1 (median 8.5, ran ge 1-270) (P < .05 and P < .005, respectively). The persistence of the nucl eated red blood cell count elevation was also longer in groups 3 (median 4 days, range 1-19 days) and 2 (median 2.5 days, range 1-7 days) than in grou p 1 (median 1 day, range 1-8 days). Neonates in group 3 also had lower plat elet count, hemoglobin value, hematocrit value, and white blood cell count. The umbilical cord artery bicarbonate level was the strongest independent determinant of the peak nucleated red blood cell count and persistence of n ucleated red blood cell elevation (r(2) = 0.27, P < .001 and r(2) = 0.47, P < .0001). CONCLUSION: Increasing abnormality of arterial and venous flows in fetuses with intrauterine growth restriction is associated with increasing nucleate d red blood cell count at birth. Metabolic acidemia rather than altered Po, associated with this circulatory slate appears to be the main determinant of the rise in nucleated red blood cells.