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Fetomatemal incompatibility for human platelet antigens (HPA) may immunize the mother and cause alloimmune thrombocytopenia in the infant. Most cases are caused by HPA-1a antibody but antibodies to a number of other platelet antigens or, possibly, HLA antibodies are responsible for some cases. Most cases are diagnosed after birth; hence the terminology neonatal alloimmune thrombocytopenia (NAIT). However, the condition develops in utero and the fetus may be severely affected. The first affected infant is usually unexpected and initial diagnosis is made by exclusion of other causes of neonatal thrombocytopenia. The diagnosis is confirmed by detection of a maternal platelet alloantibody against the father's platelets. Management of subsequent pregnancies concentrates on protecting the fetus from thrombocytopenic bleeding, especially intracranial hemorrhage (ICH). A major advance is the use of fetal blood sampling for accurate diagnosis and for assessment of the severity of fetal thrombocytopenia. Options for management include maternal treatment with IVIG and/or corticosteroids. For cases considered to be at high risk of ICH, fetal platelet transfusions are the preferred form of management. After birth the infant is still at risk for intracranial hemorrhage. The platelet count may continue to fall after delivery and the infant's platelets should be counted daily. If there is a perceived risk of bleeding, a platelet transfusion should be given, or high dose IVIG if platelets are not available. Compatible donor platelets or maternal platelets can be used. Maternal platelets should be plasma-reduced or washed with saline. |
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