haemolytic disease of the newborn

the condition resulting from destruction (haemolysis) of the red blood cells of the fetus by antibodies in the mother's blood passing through the placenta. This most commonly happens when the red blood cells of the fetus are Rh positive (i.e. they have the rhesus factor) but the mother's red cells are Rh negative. The fetal cells are therefore incompatible in her circulation and evoke the production of antibodies. This may result in very severe anaemia of the fetus, leading to heart failure with oedema (hydrops fetalis) or stillbirth. When the anaemia is less severe the fetus may reach term in good condition, but the accumulation of the bile pigment bilirubin from the destroyed cells causes severe jaundice after birth, which may require exchange transfusion. If untreated it may cause serious brain damage (see kernicterus).

A blood test early in pregnancy enables the detection of antibodies in the mother's blood and the adoption of various precautions for the infant's safety. Some cases of predictably very severe haemolytic disease have been successfully treated by intrauterine transfusion. The incidence of the disease has been greatly reduced by preventing the formation of antibodies in a Rh negative mother. If at birth or after an abortion the baby's blood is found to be incompatible with the mother's (i.e. Rh positive) she is given an injection of Rh antibody (anti-D immunoglobulin). This rapidly destroys any Rh positive fetal cells so that they do not remain long enough to stimulate antibody production in her blood (which could affect her next pregnancy).