Abstract: Objective To investigate the relationship between the IgG antibody titers of type O blood pregnant women and the incidence of ABO hemolytic disease of newborns (HDN).Methods The blood samples of pregnant women and their husband were tested as a matter of routine to identify the ABO and Rh D blood type.The parents with ABO blood group incompatibility would be tested the IgG anti-A/anti-B antibody titer by micro column gel coombs test.The hemolytic diseases of their newborn were also detected.Results Among 513 pregnant women, 271 pregnant women's antibody titer was less than 1:32, accounting for 52.8%.Fifty-eight cases' antibody titer was 1:64, accounting for 26.3%.Sixty-six cases' antibody titer was 1:128, accounting for 12.9%.Fourty-one cases' antibody titer was more than 1:256, accounting for 8.0%.The IgG anti A/B titer was significantly increased with the increase of number of pregnancies and age of pregnant women (P<0.05).Among 513 cases, 52 cases suffered from HDN.The incidence HDN was 10.1%.There was positive correlation between IgG anti A/B titer and ABO hemolytic disease of the newborn (P<0.05).Conclusion The anti A (B) titer in serum of pregnant women is closely related to the pathogenesis of HDN.To detect the ABO antibody titer of pregnant women is helpful to timely diagnose the HDN.Moreover, it is significant to reduce the incidence of hemolytic disease caused by maternal and neonatal blood group incompatibility.