Human platelet antigen antibody induction in uncomplicated pregnancy is associated with HLA sensitization.

BACKGROUND Alloimmunization against human platelet antigens (HPAs) during pregnancy is rare but can lead to severe bleeding disorders, such as fetal and neonatal alloimmune thrombocytopenia. STUDY DESIGN AND METHODS In a cohort of 241 uncomplicated pregnancies, we investigated the immunogenicity of HPA mismatches and correlated HLA sensitization with HPA antibody formation. HPA antibodies were measured with a Luminex-based multiplex assay. RESULTS HPA mismatches were observed in 109 of 241 pregnancies (45%), but child-specific HPA antibodies were only found in two of 109 cases (2%), indicating a low immunogenicity. Only nine of 241 women (4%) had detectable HPA antibodies. HLA sensitization was identified as a strong and independent predictor for HPA antibody formation (hazard ratio, 10.2; 95% confidence interval, 1.8-193; p = 0.006), whereas the number of pregnancies was not. CONCLUSION Our observational data indicated a low immunogenicity of HPA and suggest that a broader immune response-inferred by HLA sensitization-is probably associated with HPA antibody induction.