Testing of maternal sera in pregnancies at risk for neonatal alloimmune thrombocytopenia

The utility of prenatal testing of maternal serum for platelet-reactive antibody was assessed in 25 women at risk of delivering infants with neonatal alloimmune thrombocytopenia (NAT). Seventeen women were incompatible with their husbands for the PlA1 antigen and three for Baka; in five families, no demonstrable platelet-specific antigen incompatibility was found. Analysis of the clinical outcome demonstrated that women with platelet-specific antibody detectable in any of the assays at any time during gestation were at risk of delivering thrombocytopenic infants (neonatal platelet count 31,250/microliters if mother did have antibody, as compared with 138,750/microliters if she did not; p less than 0.005). When only PlA1-incompatible pregnancies were examined, this association remained significant (mean neonatal platelet count in infants exposed to anti-PlA1, 34,285/microliters; that in infants not so exposed, 243,000/microliters; p less than 0.001). Changes in antibody strength throughout pregnancy did not correlate with the severity of NAT. The combination of the antigen-capture enzyme-linked immunosorbent assay and the indirect immunofluorescence test appeared to be most sensitive in detecting relevant platelet-specific alloantibodies. It is concluded that the detection of platelet-specific alloantibody in maternal serum in pregnancies at risk for NAT predicts moderate to severe NAT. However, the failure to detect such antibody does not always predict a normal neonatal platelet count.