A potentially serious disease of the fetus and newborn, characterised by haemolytic ANAEMIA (excessive destruction of red blood cells) and JAUNDICE. If severe, it may be obvious before birth because the fetus develops heart failure and becomes very oedematous (see OEDEMA),– so-called hydrops fetalis. It may become noticeable only on the first day or two of life as jaundice and anaemia. The disease is due to blood-group incompatibility between the mother and baby, the commonest type being rhesus incompatibility (see BLOOD GROUPS). It may occur when a rhesus-negative mother's immune system has already been sensitised to produce rhesus antibodies, either by the previous delivery of a rhesus-positive baby, a miscarriage or a mismatched blood transfusion. These antibodies cross over into the fetal circulation and attack any of the fetal red blood cells which contain the rhesus antigen on their surface (that is, if the baby happens to be rhesus positive), causing the red cells to break open – HAEMOLYSIS.
The infant's serum BILIRUBIN – the bilirubin present in the blood – and its HAEMOGLOBIN concentration are measured frequently so that treatment can be given before levels occur that could cause brain damage. Safe bilirubin concentrations depend upon the maturity and age of the baby, so reference charts are used.
Moderately high bilirubin concentrations may be treated with PHOTOTHERAPY; extra fluid is given to prevent dehydration and to improve bilirubin excretion by shortening the gut transit time. Severe jaundice and anaemia may require EXCHANGE TRANSFUSION, removing the baby's blood (repeatedly removing 10 millilitres at a time over an hour or two) and replacing it with rhesus-negative fresh bank blood. Haemolytic disease of the newborn secondary to rhesus incompatibility has become less common since the introduction of anti-D (Rho) immunoglobulin given routinely to rhesus-negative mothers after the birth of a rhesus-positive baby or after threatened abortions, antepartum haemorrhages, miscarriages, and terminations of pregnancy.
Occasionally haemolytic disease is caused by ABO incompatibility or that of rarer blood groups.