Neonatal alloimmune thrombocytopenia (NAITP, NAIT, NATP or NAT) is a disease that affects babies in which the platelet count is decreased because the mother's immune system attacks her fetus' or newborn's platelets. A low platelet count increases the risk of bleeding in the fetus and newborn. If the bleeding occurs in the brain, there may be long-term effects. Platelet antigens are inherited from both mother and father. NAIT is caused by antibodies specific for platelet antigens inherited from the father but which are absent in the mother. Fetomaternal transfusions (or fetomaternal hemorrhage) results in the recognition of these antigens by the mother's immune system as non-self, with the subsequent generation of allo-reactive antibodies which cross the placenta. NAIT, hence, is caused by transplacental passage of maternal platelet-specific alloantibody and rarely human leukocyte antigen (HLA) allo-antibodies (which are expressed by platelets) to fetuses whose platelets express the corresponding antigens. NAIT occurs in somewhere between 1/800 and 1/5000 live births. More recent studies of NAIT seem to indicate that it occurs in around 1/600 live births in the Caucasian population.
Signs and symptoms The diagnosis of NAIT is usually made after an incidental finding of a low platelet count on a blood test or because of bleeding complications ranging from bruising or petechiae to intracranial hemorrhage in the fetus or newborn. Frequently, the reduction in platelet count is mild and the affected neonates remain largely asymptomatic. NAIT is the commonest cause of a very low platelet count, and the commonest cause of intracranial haemorrhage in the term neonate. In case of severe thrombocytopenia, the neonates may exhibit bleeding complications at or a few hours after delivery. The most serious complication is intracranial hemorrhage, leading to death in approximately 10% of symptomatic babies or neurologic sequelae in 20% of cases. 80% of intracranial hemorrhages occur before birth. After birth the greatest risk of bleeding is in the first four days of life.
Related conditions Immune thrombocytopenic purpura (ITP), sometimes called idiopathic thrombocytopenic purpura is a condition in which autoantibodies are directed against a patient's own platelets, causing platelet destruction and thrombocytopenia. Anti-platelet autoantibodies in a pregnant woman with immune thrombocytopenic purpura will attack the patient's own platelets and will also cross the placenta and react against fetal platelets. Therefore, ITP is a significant cause of fetal and neonatal immune thrombocytopenia. Approximately 10% of newborns affected by ITP will have platelet counts <50,000 μL−1 and 1% to 2% will have a risk of intracerebral hemorrhage comparable to infants with NAIT. Mothers with thrombocytopenia or a previous diagnosis of ITP should be tested for serum anti-platelet antibodies. A woman with symptomatic thrombocytopenia and an identifiable anti-platelet antibody should be started on therapy for their ITP which may include steroids or IVIG. Fetal blood analysis to determine the platelet count is not generally performed as ITP-induced thrombocytopenia in the fetus is generally less severe than NAIT. Platelet transfusions may be performed in newborns, depending on the degree of thrombocytopenia.
Other conditions causing a low platelet count Other conditions that can cause a low platelet count in the neonate include bacterial and viral infection, disseminated intravascular coagulation and other rare congenital conditions associated with a low platelet count.
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