Neonatal alloimmune thrombocytopenia (NAIT), or fetal maternal alloimmune thrombocytopenia (FMAIT), is a rare disease caused by maternal alloimmunization to inherited paternal human platelet antigens (HPA) expressed on fetal platelets (see Note 1). Maternal anti-HPA IgG antibodies can cross the placenta and cause the immune destruction of fetal platelets. Severe fetal thrombocytopenia can result in intracerebral haemorrhage (ICH) or death in utero. Unlike hemolytic disease of the newborn, NAIT can occur in the first pregnancy (1). Most cases are diagnosed post-delivery and the incidence of the disorder is about 1 in 2000 live births, which accounts for about 10% of all neonatal thrombocytopenias (platelets > 100×10⁹/L) (2). Spontaneous in utero intracranial hemorrhage occurs in approx 10% of NAIT cases and can develop as early as 20 wk of gestation. In the absence of routine antenatal screening for maternal anti-HPA antibodies, the first affected baby is usually diagnosed postnatally or in utero after intracranial hemorrhage has already occurred. Antenatal management can be planned in advance for women known to have anti-HPA antibodies.