The human platelet antigen system (HPA1) isglycoprotein (CD61) of human platelets. Clinically HPA1ais the most immunogenic HPA. Neonatal alloimmunethrombocytopenia (NAITP) is caused by transplacentaltransfer of maternal IgG antibody inherited from the fatherresulting in thrombocytopenia especially intracranialhemorrhageCross sectional study was done on 6773 pregnantladies that were selected randomly from Al-Galaamaternity hospital, the prevalence of HPA1bb is 3.8% inthis study by flowcytometry and ELISA, 9% of them werealloimmunized as detected by MAIPA test (MonoclonalAntibody Immobilization of Platelets Antigen assay),NAITP is reported in 1:1355. All cases which were bornwith NAITP did not need medical intervention like platelettransfusion, and on the other hand all mothers withthrombocytopenic newborns due to NAITP expressingHLA DR B3*0101.