Neonatal thrombocytopenia and hidden maternal autoimmunity.

Severe transient thrombocytopenia was observed in 17 newborns delivered by 11 mothers who persistently exhibited normal platelet counts and had no previous immunological or platelet disorder. Maternofetal alloimmunization as well as other causes for fetal thrombocytopenia were ruled out. A specific circulating autoantibody directed against the platelet glycoprotein Ib/IX complex was found in 10/11 mothers and in 3/4 offspring. After delivery, maternal compensated thrombocytolysis and/or hypersplenism were demonstrated by 111Indium labelled platelet studies in 10/11 women. The association of a compensated thrombocytolysis and of a specific maternal circulating antiplatelet autoantibody makes likely the diagnosis of mild maternal chronic autoimmune thrombocytopenic purpura (AITP) only expressed by the fetal or neonatal thrombocytopenia. The finding of anti-IbIX autoantibody in control women who gave birth to neonates without thrombocytopenia raises the question of the incidence and clinical significance of such antibodies which could be natural autoantibodies as well as associated with compensated thrombocytolysis or with overt immune thrombocytopenia. The cause of the discrepancy between the fetal and maternal platelet status, which could be explained by a different conformational state of fetal as compared to adult GP Ib/IX, deserves further investigation.