Oxygen transport to the tissues can be broadly illustrated using the oxyhaemoglobin dissociation curve which depicts the affinity of oxygen with haemoglobin, which is the main oxygen-transporting protein in the blood. The high fraction of foetal haemoglobin at birth is a reflection of the intrauterine role of the foetal haemoglobin, which is to facilitate the transfer of oxygen from the placenta to the foetal circulation, as foetal haemoglobin has a higher affinity with oxygen compared to the adult type of haemoglobin. An increased partial arterial pressure of carbon dioxide, low pH and high temperature can also shift the oxyhaemoglobin curve to the right. The right shift of the curve and the partial pressure at which haemoglobin is 50% saturated with oxygen are anchor points of an individual subject’s oxyhaemoglobin curve, which among other can give information on respiratory disease severity. Other non-oxygen carrying haemoglobin subtypes which are clinically important in neonatal medicine are the carboxy-haemoglobin which is a marker of oxidative disease, and the meth-haemoglobin which is typically monitored during the administration of inhaled nitric oxide.