Management of severe alloimmune thrombocytopenia in the newborn.

Petechiae or echymoses and severe thrombocytopenia (< 20 × 10 platelets/litre) is a worrying and serious condition in newborn infants. Rapid correction of the platelet count is essential to prevent cerebral bleeding and associated life long disability, and this should be combined with laboratory investigations to confirm the clinical diagnosis. Prospective studies have revealed that the most likely cause of severe thrombocytopenia in a term and otherwise healthy neonate is immune mediated destruction of fetal/neonatal platelets by maternal alloantibodies. 2 Antibodies can be formed against human platelet alloantigens (HPAs) 4 present on fetal but not maternal platelets (table 1). Leakage of fetal platelets and possibly other HPA alloantigen expressing fetal cells into the maternal circulation during pregnancy can stimulate the mother’s immune system to produce IgG alloantibodies against “non-self” HPAs inherited from the father. Maternal HPA alloantibodies of the IgG class cross the placenta and bind to fetal platelets, shortening their survival.