Fetal and neonatal alloimmune thrombocytopenia.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is one of the major causes of both severe thrombocytopenia and intracranial haemorrhage in fetuses and term neonates. The incidence of FNAIT is estimated to be one in 1000-2000 births. FNAIT is caused by maternal immunoglobulin G alloantibodies, which cross the placenta and are directed against human platelet antigens (HPA) on fetal platelets. In Caucasian individuals, the immunodominant antigen is HPA-1a, which is responsible for approximately 85% of FNAIT cases. The most feared complication of a low platelet count in the fetus or the neonate is intracranial haemorrhage and subsequent neurological handicaps. Over the last 15 years, there has been a gradual change in antenatal treatment, from an invasive management protocol to a less invasive management protocol to a completely non-invasive approach. However, controversy still exists over the optimal antenatal management strategy.