Red cell values on the first postnatal day during the last 16 weeks of gestation.

The hemoglobin concentration, red cell count, hematocrit, reticulocyte count, and red cell size distribution were determined on skin prick blood obtained on the first postnatal day from infants born at various stages of gestation, from week 24 to term. During this period the hemoglobin concentration and hematocrit remained constant, around 19 gm/100 ml and 60%, respectively. The mean corpuscular volume decreased progressively, with a corresponding rise in the red cell count. The reticulocyte count decreased progressively from 9.6% to 3.7% during the period of observation. The red cell size distribution (Price Jones) curve was markedly shifted to the macrocytic side at 24-25 weeks. Thereafter, cells larger than 102 mu3 decreased gradually, while the percentage of smaller cells increased. These observations are not consistent with the hypothesis of a progressive decrease in the supply of oxygen to the fetus during the later stages of gestation, to which the fetus adapts by increasing its hemoglobin concentration.