A prospective study of maternal anti-HPA 1a antibody level as a potential predictor of alloimmune thrombocytopenia in the newborn

Abstract
Background Neonatal alloimmune thrombocytopenia is most commonly due to transplacental passage of maternal anti-HPA 1a antibodies. A prospective study was carried out to evaluate the pattern and quantity of maternal anti-HPA 1a antibodies in order to predict the level of thrombocytopenia in the neonates. Design and Methods A monoclonal antibody immobilization of platelet antigen assay was used to detect antibodies in maternal samples from 1,990 HPA 1bb women. HLA DRB3*0101 typing was performed in all immunized women by sequencing the HLA DRB3 gene when present. Results Primary immunization more often took place in connection with delivery than during the first pregnancy. There was a strong correlation between maternal antibody levels and the platelet counts in the newborn (R2=0.49, pp92 or more of 147 = 0.003). The anti-HPA 1a antibody level regularly increased after delivery. Conclusions Maternal anti-HPA 1a antibody levels in weeks 22 and 34 of pregnancy are good predictors of the degree of thrombocytopenia in the newborn both in the first and subsequent pregnancies. Most mothers became immunized at the time of delivery.

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