Introduction: It is well known that HPA-1a antibodies lead to fetal and neonatal alloimmune thrombocytopenia (FNAIT), and an association with reduced birthweight in boys has been reported. Although it remains unclear whether HLA antibodies cause FNAIT, an association between HLA class I antibodies and reduced birthweight in FNAIT neonates has been observed. The aim of this study was to investigate the incidence of platelet antibodies among Chinese women and the impact of maternal alloimmune antibodies on birthweight among healthy neonates. Material and methods: In this retrospective observational cohort study, platelet antibody screening was performed among women hospitalized for delivery from March 2019 to November 2020. A portion of each serum sample was used to distinguish How to cite this article: Xue Y, Xin W, Li C, et al. Maternal alloimmune antibodies against HPA and HLA class I antigens are associated with reduced birthweight among healthy neonates delivered by Chinese women.