Friday August 28, 2009 (pediatric pearl)
Fetal haemoglobin

Fetal haemoglobin (which is present in fetal life and up to 3 months following birth) is not able to deliver oxygen to the tissues as efficiently as normal haemoglobin because the oxy-haemoglobin dissociation curve is shifted to the left causing oxygen to be released less readily. Neonates have a higher haemoglobin concentration (17 g/dl) and blood volume and this together with the increased cardiac output compensates for the decreased release of oxygen from haemoglobin in the tissues. Replacement of fetal haemoglobin with adult haemoglobin begins at 2-3 months of age and this period is known as physiological anaemia as haemoglobin concentrations may fall to 11 g/dl. Anaemia sufficient to jeopardise oxygen carrying capacity of the blood is possible if the haemoglobin concentration is less than 13 g/dl in the newborn and less than 10 g/dl in the infant under 6 months of age.