Analysis of rates of globin synthesis in normal human fetuses and neonates and in twins.

The factors responsible for the switch from gamma- to beta-globin synthesis, which occurs in man in the perinatal period, are still unknown. In this study the relationship of fetal maturity (as measured by gestation age and fetal weight) to changing rates of globin synthesis was analyzed. The relationship of rates of erythropoiesis to the switch was also analyzed. Rates of globin chain synthesis were studied in blood from fetuses from 10-41 wk gestation, in neonates up to 6 mo of age, and in a series of twins from 29-40 wk gestation. The beta/gamma-globin synthesis ratio in fetal blood remained relatively constant until 30-34 wk gestation when an increase in beta-globin production was observed. Adult levels of globin synthesis were present in neonates at 6-9 wk after birth. The gamma/alpha-globin synthesis ratio showed a reciprocal change, falling after 30 wk gestation. Globin synthesis ratios in fetuses and neonates from 32-41 wk post-conception showed a significant correlation with age (beta/gamma: p less than 0.001; beta/alpha:p less than 0.001; gamma/alpha: p less than 0.05), and there were significant correlations between the beta/alpha and beta/gamma synthesis ratios and weight (p less than 0.05 for both ratios). Globin synthesis ratios in 12 sets of twins from 29-40 wk gestation were generally within the normal range for gestational age. However, the switch to beta-globin production was more advanced than expected from weight for some of these babies.