Triplets with neonatal alloimmune thrombocytopenia due to antibodies against human platelet antigen 1a

BACKGROUND: Neonatal alloimmune thrombocytopenia (NAIT) has been reported only rarely in twins and not at all, to our knowledge, in triplets. CASE REPORT: Nonidentical triplets were born with severe thrombocytopenia. Nadir platelet (PLT) counts were 17 × 10⁹ , 12 × 10⁹ , and 10 × 10⁹ /L. NAIT was confirmed by an incompatibility for human PLT antigen (HPA)-1a and the presence of maternal anti-HPA-1a. The maternal genotype was HPA-1bb and the paternal genotype was HPA-1aa; thus, all children were affected. RESULTS: PLT counts for each infant improved with the administration of random-donor PLT transfusions. All three infants also received intravenous immunoglobulin. None had major bleeding. A small isolated subependymal hemorrhage was found incidentally in one infant; this remained stable on repeat imaging. CONCLUSIONS: This is the first report of triplets with NAIT. Anti-HPA-1a is sufficiently potent to affect three infants simultaneously. Random-donor PLTs were effective in improving PLT counts in all three infants.