Haemoglobin synthesis during development

• haemoglobin synthesis during development
  
  
  • fetal haemoglobin, haemoglobin (Hb) F, (alpha 2 gamma2) represents 90-95% of all haemoglobin by 34-36 weeks gestation
    
    
  • adult haemoglobin, Hb A, (alpha 2 beta 2) accounts for 4-13% of total haemoglobin in the fetus
  • after 34 weeks gestation, Hb A production increases significantly as Hb F production falls
    
    
  • at term, Hb F represents 53-95% of all haemoglobin with Hb A levels reaching 20-30%
    • in addition to being increased in some haemoglobinopathies, increased levels of Hb F can be seen in infants who are small for gestational age, who have experienced chronic hypoxia or who have trisomy 13
    • haemoglobin F percentage remains static for the first 2 weeks of life and then decreases by approximately 3% per week when erythropoiesis recommences and is normally <2-3% of total haemoglobin by 6 months of age
    • Hb A becomes the predominant haemoglobin by 3 months of age, although this switch may be delayed in sick preterm infants
      
      
  • haemoglobin A2 (alpha2 delta 2) is produced in small amounts from birth and usually reaches adult levels by 6 months of age, although it can rise further for the first 1-2 years of life
    • Hb A2 and Hb Bart,s may be detected in normal infants born at term
      
      
  • the pattern of haemoglobin synthesis during development explains why alpha chain abnormalities cause clinical problems from early fetal life and why beta chain abnormalities may be difficult to diagnose in the neonatal period

Reference:

• (1) Significant haemoglobinopathies: guidelines for screening and diagnosis. British Journal of Haematology 2010: 149 (1): 35-49