Introduction

Neonatal alloimmune thrombocytopenia—caused by movement of maternal alloantibodies directed against fetal platelet antigens across the placenta—is the most common cause of severe neonatal thrombocytopenia.1 These alloantibodies cause thrombocytopenia, which may result in intracranial haemorrhage.2 3 Most cases arise unexpectedly, and prompt diagnosis and treatment are essential to reduce the chances of death and disability caused by the haemorrhaging.4 5 Neonatal alloimmune thrombocytopenia should be strongly suspected in cases of neonatal thrombocytopenia with no evidence of sepsis, systemic disease, or skeletal anomalies associated with thrombocytopenia, and where maternal idiopathic thrombocytopenic pupura has been excluded. We describe two cases with typical clinical presentations in which standard methods for detection of maternal antibodies gave negative results, and we show that empirical treatment with human platelet antigen 1a negative platelets yielded successful outcomes in both cases.

Case 1

A two day old girl presented with several left sided and secondary generalised tonic-clonic seizures. She had been delivered normally at full term, after an uneventful gestation. Neurological examination between seizures had normal results, and otherwise she was completely well.

Her platelet count was 5x10⁹/l, haemoglobin concentration was 158 g/l, and white cell count was 16.7x10⁹/l. A magnetic resonance scan showed fresh extensive haemorrhage in the interhemispheric fissure and sulci (1). The brain and ventricles were normal. Viral swabs and culture showed no infectious cause for the thrombocytopenia. The baby's mother had a normal platelet count.