Neonatal alloimmune thrombocytopenia due to anti-HPA-5b (Br^a)

Neonatal alloimmune thrombocytopenia (NAIT) results from maternal immunization against fetal platelet antigens and can occur during the first pregnancy. The most common complications of NAIT are neonatal thrombocytopenia, intracerebral hemorrhage, and fetal death. Most cases of NAIT in Causasians are caused by anti-HPA-1a (Pl^A1). Anti-HPA-5b (Br^a) accounts for only 4.3 percent of all NAIT cases. NAIT due to anti-HPA-5b is thought to be milder and have fewer complications than NAIT caused by anti-HPA-1a because of the lower number of HPA-5b antigenic sites per platelet. This report describes a severe case of NAIT due to anti-HPA-5b that was treated by intrauterine platelet transfusion.