Prevention programmes against Rh alloimmunization are now so widespread as to be universal in the developed world. Accordingly, there has been a dramatic decline in the incidence of fetal anaemia secondary to this cause, along with relative growth in the importance of alloimmunization due to other antibodies, particularly Kell. Antibodies to the Kell group of antigens, in particular K1, can cause profound fetal anaemia leading to hydrops and fetal demise unless appropriate and timely intervention is undertaken.