Observations on the Change from Foetal to Adult Erythropoiesis

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Abstract
The individual red cells of a fetus or newborn child can be classified according to their reaction to acid hydrolysis as of fetal, intermediate, or adult type. Intermediate cells contain a mixture of haemoglobins A and F. Examination of blood from early and late fetuses and infants shows that (a) fetal cells are last formed in the first week of life, (b) intermediate cells appear before the 34th week of gestation and are last formed in the 16th week of life, and (c) adult cells first appear at the 37th week of gestation. Evidence is given that the marrow can produce Hb F in gradually declining amounts from the onset of its activity until the 16th week of life. There are indications that the capacity of the liver to manufacture Hb A increases in the perinatal period. The change from fetal to adult erythropoiesis is a gradual one and is probably the result of a gene-controlled maturation of the intracellular synthetic mechanism.