Abstract
Foetal/neonatal alloimmune thrombocytopaenia (NAIT) results from maternal alloimmunisation against foetal platelet antigens inherited from the father and different from those present in the mother, and usually presents as a severe isolated thrombocytopaenia in otherwise healthy newborns. The incidence has been estimated at 1/800 to 1/1 000 live births. NAIT has been considered to be the platelet counterpart of Rh Haemolytic Disease of the Newborn (RHD). Unlike RHD, NAIT can occur during a first pregnancy. The spectrum of the disease may range from sub-clinical moderate thrombocytopaenia to life-threatening bleeding in the neonatal period. Mildly affected infants may be asymptomatic. In those with severe thrombocytopaenia, the most common presentations are petechiae, purpura or cephalohaematoma at birth, associated with major risk of intracranial haemorrhage (up to 20% of reported cases), which leads to death or neurological sequelae. Alloimmune thrombocytopaenia is more often unexpected and is usually diagnosed after birth. Once suspected, the diagnosis is 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 be delayed by biological confirmation of the diagnosis (once the diagnosis is 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.
Highlights
Noglobulin 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 [1]
Foetal/neonatal alloimmune thrombocytopaenia (NAIT) is a disorder caused by foetomaternal platelet incompatibility that usually presents as severe isolated thrombocytopaenia in otherwise healthy newborns
As thrombocytopaenia when moderate is 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 [5]
Summary
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 [6,7,8]. ICH has been reported in NAIT (whatever the platelet antigen involved, see Aetiology) and is usually present at birth. Anti HPA-1a and -3a immunisation induce severe neonatal thrombocytopaenia (see Aetiology) [9]. The infant may be symptomless, with thrombocytopaenia discovered incidentally, even in case of HPA-1a alloimmunisation. Among the platelet-specific alloantigens, HPA-1a antigen is the form most commonly involved in NAIT in Caucasians [21], followed (at much lower frequency) by HPA5b [10]. A better understanding of the immune response to platelet alloantigens would allow for a better definition and appropriate management of pregnant women at high risk
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