[Neonatal alloimmune thrombocytopenia].

Neonatal alloimmune thrombocytopenia (NAIT) is induced by maternal antibodies directed against fetal platelet alloantigens. Platelet alloantigens involved in NAIT has been documented in HPA-1 (a,b), -2a, -3(a,b), 4(a,b), -5(a,b) and the low frequency alloantigens (Tu/Ca, Mo, Sra,...). Alloimmunization to platelet antigens occurs in 0.94% of pregnant Japanese women. The frequency of NAIT is estimated at 1:3300 births. Incompatibility for HPA-4 is the major (80%) cause of NAIT, followed by HPA-3a (15%) in this population. HPA-5b induced NAIT is rare, despite that the antibody is found often (0.7%) in pregnant women. Since, about half of the cases of NAIT occur during the first pregnancy, it is impossible to anticipate intracranial hemorrhage in many instances. Mild, asymptomatic cases often requires no specific therapy. Compatible platelets irradiated to prevent post-transfusion graft-vs-host disease should be transfused to any infants with severe hemorrhage and can help to prevent bleeding in asymptomatic infants. The administration of intravenous immunoglobulin in NAIT fetus/newborns or pregnant women is worthy of trial.