Haemolytic disease can be fatal to a newborn child. It is caused by the incompatibility of the mothers' blood with that of the foetus with respect to the rhesus factor. The most severe form of haemolytic disease, the edematous form, generally causes stillbirth, or death a few hours after birth (which is often premature). The icteric form, if not adequately treated, may cause brain damage and anaemia and retard the child's development. The mildest form, congenital anaemia, is curable if the necessary medicine and expertise is available. The risk of haemolytic disease increases with succeeding pregnancies, and also in pregnancies following abortion.
10 to 15% of the Irish population is rhesus negative.