Abstract: Objective To explore the risk factors of macrosomia in patients with gestational diabetes mellitus, and its effects on pregnancy outcome. Method A total of 498 women with gestational diabetes mellitus in The Third Affiliated Hospital of Zhengzhou University from February 1, 2018 to January 31, 2019 were enrolled and were divided into the macrosomia group(65 cases) and the control group(433 cases) according to the weight of newborns. The clinical data of the two groups were retrospectively reviewed. Result The prevalence of macrosomia was 13. 1%(65/498). Multivariate Logistic regression analysis showed that fasting blood glucose(FPG) value in 75 g oral glucose tolerance test(OGTT), preconception body mass index and gestational weight gain were independent risk factors for macrosomia in patients with gestational diabetes mellitus(P< 0. 05). Compared with the control group,there were no significant differences between two groups as in maternal age, residence, assisted reproductive technology, gestational week of delivery, parity, family history of diabetes, history of macrosomia and insulin injection treatment(P> 0. 05). ROC curve analysis revealed that in pregnant women with gestational diabetes mellitus, the AUC of FPG in 75 g OGTT, preconception BMI and gestational weight gain in predicting macrosomia was 0. 699, 0. 632, 0. 675, respectively, and the AUC of the combined prediction of macrosomia was 0. 786. The cut-off value of each indicator in predicting macrosomia was 5. 185 mmol/L, 23. 02 kg/m², 13. 75 kg,respectively. In terms of pregnancy complications, the incidence of postpartum hemorrhage in the macrosomia group was significantly higher than that in the control group(P< 0. 05). There was no significant difference in neonatal outcomes between the two groups(P> 0. 05).Conclusion (1) Among pregnant women with gestational diabetes mellitus, FPG in 75 g OGTT, preconception BMI and gestational weight gain were independent risk factors for macrosomia;(2) When FPG in 75 g OGTT > 5. 185 mmol/L, preconception BMI > 23. 02 kg/m² or gestational weight gain > 13. 75 kg, the risk of macrosomia was significantly increased in gestational diabetes mellitus population;(3) Macrosomia increase the risk of postpartum hemorrhage in pregnant women with gestational diabetes.