The HbA/HbA2 ratio in newborns and its correlation with fetal maturity.

The relative amounts of HbF, HbA and HbA2 were determined in about 1000 newborns and their parents. In newborns the mean value of HbA2 was 0.27 +/- 0.02% and that of HbF 74.69 +/- 0.25%. The ratio HbA/HbA2 was estimated at different gestational ages and was found to range from 101 at 32 weeks gestation to 76 at 45 weeks, indicating that the relative amount of HbA2 increases with fetal maturation. The correlations between the levels of the different haemoglobins and various indexes of fetal maturation (gestational age, birth weight, crown-heel length and head circumference) are also given.