Rhesus disease is a condition in which antibodies develop in your bloodstream against the baby''s red blood cells. This can only occur if your blood group is rhesus negative and the baby''s is rhesus positive. In this situation, if you are ''sensitized'' from a previous pregnancy, blood leaking from the baby''s circulation to yours (as inevitably happens during pregnancy) will cause more antibodies to be formed to damage the baby''s cells. This can make the baby quite anaemic, and in severe cases the baby might need blood transfusions while in the womb. In milder cases, the baby might need a transfusion after delivery, or ''phototherapy'' to break down jaundice in the baby''s skin.