L’allo-immunisation érythrocytaire fœtomaternelle dans le système ABO reste la principale cause des maladies hémolytiques du fœtus et du nouveau-né. Sa gravité est généralement moindre que l’allo-immunisation RhD (Rhésus). Nous rapportons 3 cas cliniques qui nous rappellent que l’allo-immunisation ABO peut parfois induire une maladie hémolytique du nouveau-né sévère. La prévention des complications de ces maladies hémolytiques impose une prise en charge précoce et adaptée avec une photothérapie intensive. Tous les nouveau-nés dont la mère a un groupe sanguin O devraient bénéficier d’une détermination de leur groupe sanguin et d’un test direct à l’antiglobuline (test de Coombs) au sang du cordon. Une bonne connaissance des facteurs de risque et une surveillance clinique attentive sont indispensables pour une prise en charge adéquate. Cette vigilance est encore plus importante en cas de retour à domicile précoce après la naissance.

ABO allo-immunization is the most frequent hemolytic disease of the newborn and ABO incompatibility is present in 15–25 % of pregnancies. True ABO alloimmunization occurs in approximately one out of 150 births. Intensity is generally lower than in RhD allo-immunization. We report on three cases showing that ABO allo-immunization can lead to severe hemolytic disease of the newborn with potentially threatening hyperbilirubinemia and complications. Early diagnosis and adequate care are necessary to prevent complications in ABO incompatibility. A direct antiglobulin test is the cornerstone of diagnosis and should be performed at birth on cord blood sampling in all group infants born to O mothers, especially if of African origin. Risk factor analysis and attentive clinical monitoring during the first days of life are essential. Vigilance is even more important for infants discharged before the age of 72h. Every newborn should be assessed for the risk of developing severe hyperbilirubinemia and should be examined by a qualified healthcare professional in the first days of life. Treatment depends on the total serum bilirubin level, which may increase very rapidly in the first 48h of life in cases of hemolytic disease of the newborn. Phototherapy and, in severe cases, exchange transfusion are used to prevent hyperbilirubinemia encephalopathy. Intravenous immunoglobulins are used to reduce exchange transfusion. Treatments of severe hemolytic disease of the newborn should be provided and performed by trained personnel in neonatal intensive care units.