<prompt> When does switchover from fetal to adult hemoglobin synthesis begin14 weeks gestation30 weeks gestation36 weeks gestation710 days postnatal  <response>: Fetal Hb α2 γ2Adults Hb α2 β2During the initial fetal life, the major haemoglobin synthesized in the body is fetal haemoglobin, because, in the fetus, the chain synthesized predominantly is the γ chain.the β chain is present in only trace amount in early embryosThe rate of synthesis of y and β chains and the amount of HbA and HbF are inversely related during the intrauterine stage.As the age of the fetus increases, the synthesis of β chains and the amount of adult haemoglobin in the blood increasesAt 36 weeks of gestational age the rate of synthesis of β chain exceeds that of γ chain. This is called switch over. 