Objective Study the relationship between HLA antibodies production and the number of Gravidity.Methods A total of 856 pregnant women of first pretanal in Xiasha Hospital of Sir Run Run Shaw Hospital of Zhejiang University from Nov 2016 to Mar 2017 were recruited.The blood samples were collected during 24-28 weeks of pregnancy,and the expression of platelet-specific alloantibody was detected by solid-phase red cell adherence assay.Results There were 67 positive HLA antibody in pregnant women,and the antibody positive rate was 7.8％.There were 15 positive HLA antibody in 334 first pregnant women,14 in 214 two or more pregnancy pregnant women without abortion,10 in 107 pregnant women with once abortion,28 in 223 pregnant women with two or more abortion.The antibody positive rate respectively is 4.5％,6.5％,9.3％ and 12.6％.The production of HLA antibody was significantly associated with the numberof gravidity.Conclusion The antibody positive rate of two or more pregnancy is significantly higher than the fisrt pregnancy.