Haemoglobin and red cells in the human foetus. II. The red cells.

In a previous paper (Walker and Turnbull, 1953) we have demonstrated the haemoglobm levels and red cell count in the cord blood of the human foetus throughout pregnancy. From the 10th week to the 24th week the red cell count doubles (from 1,500,000 to 3,000,000), but the haemoglobin rises only from 9 to 15 g. After the 24th week, the red cell count continues to rise till at 40 weeks, in the well oxygenated foetus, it is just under 4,000,000 per c.mm., but the haemoglobin level is unchanged at 15 g. These findings suggest that throughout pregnancy the red cells must be becoming progressively smaller. If at 40 weeks extra red cells have been produced under the stimulus of anoxia, the haemoglobin level may be 20 g. and the red cell count 5,000,000, the haemoglobin rising by 30%, but the red cell count by only 25% over the levels found at 40 weeks in the well oxygenated foetus (15 g. and 4,000,000). These unequal rises in haemoglobin and red cells under conditions of anoxia suggested therefore that the extra cells produced are somewhat larger or contain more haemoglobin than those normally present in the blood at that time. Very little information is, however, available from other authors with regard to the characteristics of the red cells in the human foetus during pregnancy. Wintrobe and Shumacker (1935, 1936) studied 12 foetuses, obtained at hysterectomy, and three premature infants, all live born, at intervals from the 76th to the 252nd day of pregnancy. Their findings suggest that the packed cell volume increases gradually as pregnancy advances and that the red cell size and the number of immature red cells steadily diminish. Many investigators have, however, studied the red cells in the cord blood of the infant at birth (presumably at or near full-term) and some of the results are shown in Table 1. It is seen that, while the mean readings of packed cell volume vary from 50 8 to 56% the range covered (40-60%) is very similar in each series. There is reasonable agreement amongst the authors that the mean cell volume and mean cell haemoglobin are, at birth, above