Neonatal Haematology. Irene Roberts

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death (see Chapter 2).

Schematic illustration of the sites and rates of synthesis of different haemoglobins in the embryonic and fetal periods and during infancy.

      From Bain (2020)37.

Photo depicts first trimester (8 weeks) fetal blood film showing the large size of the erythroblasts typical of those derived from the yolk sac. Photo depicts second trimester (14 weeks) fetal blood film showing typical erythroblasts derived from definitive haematopoiesis.

      The production of adult haemoglobin (haemoglobin A; α2β2) begins during the second trimester and remains at low levels until 30–32 weeks post‐conception, when haemoglobin A production starts to increase concomitantly with a fall in haemoglobin F production. The net result is an average haemoglobin F in term babies of 70–80% and haemoglobin A of 25–30%.39,40 After birth, haemoglobin F falls, to approximately 2% by the age of 12 months, with a corresponding increase in haemoglobin A. The molecular control of this change from haemoglobin F to haemoglobin A is termed globin switching. In recent years, there has been considerable research into the genes involved in globin switching (e.g. BCL11A) in order to identify strategies to delay or reverse this physiological switch after birth and so maintain haemoglobin F production for children affected by severe β globin disorders such as sickle cell disease or thalassaemia major.41,42

      Red blood cell lifespan and the red blood cell membrane in the fetus and neonate

      Neonatal red blood cells, particularly in preterm babies, have a shorter lifespan than adult red blood cells. Red cell lifespan is inversely proportional to gestational age at birth. Studies over 50 years ago using isotopically labelled red blood cells estimated red blood cell lifespans for preterm infants at 35–50 days, compared with 60–70 days for term infants and 120 days for healthy adults.35 More recent estimates, using mathematical modelling and transfusion of autologous cord blood cells, have also calculated the red cell lifespan in preterm neonates to be approximately 50 days.43

Photo depicts normal blood film at term. Photo depicts normal preterm red cells at different gestational ages. Photo depicts a blood film of a normal preterm baby (born at 28 weeks’ gestation) showing a degree of erythroblastosis.

      Red blood cell metabolism in the fetus and neonate

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