[Severe neonatal alloimmune thrombocytopenia with delayed antibody detection].

Neonatal alloimmune thrombocytopenia (NAIT) is caused by maternal immunisation against a paternal antigen on fetal platelets. The antigen involved in the majority of cases is HPA-1 a (PIA1). Usually circulating platelet alloantibodies are detectable in the mother. In this report, we present a thrombocytopenic newborn with severe hemorrhagic diathesis due to materno-fetal HPA-1 a (PIA1) incompatibility. Platelet antibodies could initially not be demonstrated in the mother's serum but became detectable after four weeks. Because of the severe and protracted course of the disease, repeated platelet substitution was necessary throughout the first two months of life.