ANTI-BAKA NEONATAL ALLOIMMUNE THROMBOCYTOPENIA - POSSIBLE PREVENTION BY INTRAVENOUS IMMUNOGLOBULIN

Neonatal alloimmune thrombocytopenia (NAIT) most commonly involves ant ibodies directed against the Pl(Al) antigen, but other platelet specif ic alloantigens have been associated with it. We describe the case of a mother whose first three infants developed NAIT secondary to anti-Ba k(a) antibodies, while her fourth infant did not. The three affected i nfants were treated postnatally with platelet transfusions. The fourth infant was treated antenatally with one dose of intravenous immunoglo bulin (IVIg) given to the mother. Postpartum analysis revealed the inf ant's platelets to be Bak(a)-positive but negative for elevated IgG. M aternal serum reacted with neonatal platelets in vitro, but cord serum was negative for antiplatelet antibodies. These clinical observations do not prove the efficacy of IVIg; however, they raise several questi ons: Why wasn't this infant thrombocytopenic? Why didn't the umbilical cord contain maternal antibody? Was the single dose of IVIg responsib le for preventing NAIT? IVIg is currently under investigation in a cli nical trial evaluating its effectiveness in preventing NAIT in mothers with anti-Pl(Al) antibodies, where it has shown some success. There h ave been no reports of the use against anti-Bak(a) antibodies. We sugg est that a weekly dose schedule may not be necessary for all affected pregnancies, and antibodies with specificity other than anti-Pl(Al) ma y require less vigorous therapy.