Abstract
Hemoglobin patterns were examined in human fetuses in order to determine the onset of synthesis of adult hemoglobin in fetal red cells. In fetuses younger than 11 gestational wk, hemoglobin A could not be detected with electrophoretic techniques. A small amount of adult hemoblobin was constantly present, however, in hemolysates from fetuses older than 11 gestational wk, and it had the structural properties of adult hemoglobin A. Heterozygous fetuses had hemoglobins C and A or S and A as early as the 11th and 13th gestational wk. The findings are compatible with onset of beta hemoglobin gene action as early as the 11th gestational wk and synthesis of approximately 5% of adult hemoglobin by the end of the first and throughout the second trimester of gestation.
