Timing of Fetal Nucleated Red Blood Cell Count Elevation in Response to Acute Hypoxia

Abstract

An association between intrauterine hypoxia and increased nucleated red blood cell (RBC) counts in the peripheral circulation has long been acknowledged. Higher counts reportedly are especially likely in neurologically impaired newborn infants. This study aimed at determining the effect of acute, severe hypoxia on peripheral nucleated RBC counts in the fetal rat. Maternal animals were randomized to either 2 hours of exposure in a hypoxia chamber or exposure to room air in a control chamber. The test chamber contained 9% oxygen, 3% carbon dioxide, and balanced nitrogen. Cesarean deliveries were carried out immediately after exposure and then at intervals up to 60 hours. There were 56 fetuses in each group. No differences in nucleated RBC counts were apparent immediately after hypoxic exposure, but counts were significantly higher in the hypoxia group 12 and 24 hours after exposure. Counts in the 2 groups did not differ significantly 36, 48, or 60 hours after exposure. Like in studies of the human fetus, nucleated RBC counts decreased with advancing fetal age. Near-term fetal rats in this study exhibited a delayed but transient increase in nucleated RBC counts in the peripheral circulation after an acute hypoxic episode. It may be that an increased nucleated RBC count will be a useful marker for fetal brain injury of hypoxic origin.