However, NAIT may also be associated with other causes of thrombocytopaenia, especially maternal antiplatelet autoimmunity . is usually confirmed by demonstration of maternal antiplatelet alloantibodies directed against a paternal antigen inherited by the foetus/neonate. Post-natal management involves transfusion of platelets devoid of this antigen, and should not MJN110 be delayed by biological confirmation of the diagnosis (once the diagnosis is usually suspected), especially in case of severe thrombocytopaenia. Prompt diagnosis and treatment are essential to reduce the chances of death and disability due to haemorrhage. Due to the high rate of recurrence and increased severity of the foetal thrombocytopaenia in successive pregnancies, antenatal therapy should be offered. However, management of high-risk pregnancies is still a matter of discussion. Disease name/synonyms Foetal/neonatal alloimmune thrombocytopenia (FAIT/NAIT)  or foeto-maternal alloimmunisation thrombocytopenia (FMAIT) . Definition/diagnostic criteria Foetal/neonatal alloimmune thrombocytopaenia (NAIT) is usually a disorder caused by foetomaternal platelet incompatibility that usually presents as severe isolated thrombocytopaenia in otherwise healthy newborns. It results from destruction of the foetal platelets by maternal immunoglobulin G (IgG) antibodies elicited during pregnancy and directed against foetus-specific platelet antigens that are inherited from the father and are different from those present in the mother . Clinically, the diagnosis is usually suspected when an otherwise healthy neonate, given birth to after an uneventful MJN110 pregnancy and delivery, exhibits petechiae or widespread purpura at MJN110 birth or a few hours after birth. Visceral haemorrhages are less common. The mother is typically healthy, with no previous history of thrombocytopaenia, auto-immune disorders or ingestion of drugs. The infant has no clinical signs of contamination or malformations (see Differential diagnosis). Approximately 20% of these infants show evidence of intracranial haemorrhage (ICH) leading to death or neurological sequelae (see Prognosis). The platelet count is usually low at birth and may be associated with anaemia, secondary to bleeding. Platelet immunological investigations will confirm the maternal specific alloimmunisation (see Diagnostic methods). Epidemiology NAIT is the commonest cause of severe isolated thrombocytopaenia in the foetus and newborn. Prospective studies showed that it occurs in about 1 in 800 or 1000 live births [3,4]. Unselected cohort of neonates reported 0.9% frequency of neonatal thrombocytopaenia . Immune aetiology was exhibited in one third of these cases. As thrombocytopaenia when moderate (whatever its cause) is usually often silent, systematic neonatal blood sampling for a platelet count is the only possible way to detect neonatal thrombocytopaenia and to provide better management of the infant and subsequent pregnancies . Clinical description In the foetus, alloimmune thrombocytopaenia is considered to be the most severe thrombocytopaenia. It may occur very early during pregnancy, and in several studies, ICH has been documented before 20 weeks of gestation [6-8]. In utero, ICH accounts for approximately 50% of the reported cases of ICH in NAIT. Therefore, NAIT should be considered as a potential aetiological factor in all cases where porencephaly, ventriculomegaly and, in fact, any type of ICH is usually discovered during the foetal life. In the neonate, purpura or haematoma are the most common clinical manifestations. Visceral haemorrhages, such as gastrointestinal bleeding MJN110 or haematuria, occur less frequently. ICH has been reported in NAIT (whatever the platelet antigen involved, see Aetiology) and is usually present at birth. ICH may also occur later, if the thrombocytopaenia persists. Mildly affected infants may be asymptomatic. Anti HPA-1a and -3a immunisation induce severe neonatal thrombocytopaenia (see Aetiology) . NAIT linked to HPA-5b incompatibility seems to be less severe Tshr than HPA-1a NAIT . However, the infant may MJN110 be symptomless, with thrombocytopaenia discovered incidentally, even in case of HPA-1a alloimmunisation. Therefore, unexpected or unexplained neonatal thrombocytopaenia or early onset of severe thrombocytopaenia in both pre-term and term babies should raise the possibility of NAIT and guideline investigations accordingly. Aetiology NAIT results from maternal immunisation against foetus-specific platelet antigens. The exact mechanism underlying maternal sensitisation remains unknown..