Haemolytic disease of the newborn due to anti-M.

A patient with haemolytic disease of the newborn (HDN) due to anti-M which required exchange transfusion is described. Anti-M antibodies are usually assumed to be naturally occurring and to consist of immunoglobulin M (IgM); many however have an immunoglobin G (IgG) component. In view of this and the described occurrence of HDN, recommendations are made regarding the management of a pregnancy in which anti-M antibodies are detected.