Objective: Elevated nucleated red blood cell count in neonatal blood and Doppler-detected circulatory decompensation in fetuses with intrauterine growth restriction are associated with hypoxemia. We sought to determine the relationship between the nucleated red blood cell count at birth and the circulatory status of fetuses with intrauterine growth restriction.
Study design: Eighty-four fetuses with elevated umbilical artery pulsatility index values >2 SD above the gestational age mean and a subsequent birth weight <10th percentile were examined serially. Umbilical and middle cerebral artery pulsatility index, inferior vena cava and ductus venosus peak velocity 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 pulsatility index only; 2, middle cerebral artery pulsatility index >2 SD below the gestational age mean in addition to abnormal umbilical artery pulsatility index; 3, either peak velocity index >2 SD above the gestational age mean in the inferior vena cava and ductus venosus or pulsatile flow in the umbilical vein, or both. Nucleated red blood cells per 100 white blood cells were ascertained in a peripheral blood sample obtained within 1 hour of delivery 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 2-3180) had higher nucleated red blood cell counts than group 1 (median 8.5, range 1-270) (P <.05 and P <.005, respectively). The persistence of the nucleated 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 group 1 (median 1 day, range 1-8 days). Neonates in group 3 also had lower platelet 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 nucleated 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 nucleated red blood cell count at birth. Metabolic acidemia rather than altered PO (2 ) associated with this circulatory state appears to be the main determinant of the rise in nucleated red blood cells.