Objective：To investigate the correlation between maternal glucose and lipid metabolism indicators，triglyceride-glucose （TyG）index，and macrosomia in gestational diabetes mellitus（GDM）during the second and third trimesters of pregnancy. Methods： Based on a GDM cohort，pregnant women who underwent cesarean section delivery at the Nanjing Maternity and Child Health Hospital from January to August 2022 were selected according to strict inclusion and exclusion criteria. Participants were divided into three groups based on GDM status and newborn birth weight：normal control group（NC，n=23），GDM non-macrosomia group（GDM-N，n= 23），and GDM macrosomia group（GDM-M，n=23）. General information and glucose and lipid metabolism indicators from the second and third trimesters were collected for all three groups. The TyG index and the homeostasis model assessment of insulin resistance （HOMA-IR）were calculated. Spearman correlation analysis and linear regression models were used to analyze the correlation between maternal indicators in the second and third trimesters and GDM macrosomia. Results：In the second trimester，the GDM-M group showed elevated levels of fasting plasma glucose（FPG），glycated hemoglobin（HbA1c），and TyG index，while direct bilirubin（DBIL）and creatinine（Cr）levels were decreased. The 1 h and 2 h postprandial glucose levels were higher than the NC group but lower than the GDM-N group（P < 0.05）. In the third trimester，C-peptide（CP），triglycerides（TG），HbA1c，and TyG index were increased，and alanine aminotransferase（ALT）was higher than the NC group but lower than the GDM-N group（P < 0.05）. Spearman correlation analysis indicated that neonatal birth weight was positively correlated with maternal FPG and HbA1c in the second trimester，and with CP，HbA1c，TG，and TyG in the third trimester（P < 0.05）. Negative correlations were observed with DBIL and Cr in the second trimester（P < 0.05）. Multiple linear regression analysis revealed that maternal FPG，HbA1c，and DBIL in the second trimester，and HbA1c，TG，and TyG index in the third trimester were significant factors influencing macrosomia（P < 0.05）. Conclusion：Maternal glucose and lipid metabolism indicators and TyG index in the second and third trimesters are closely associated with the occurrence of macrosomia in GDM. HbA1c，FPG，TG，and TyG can serve as important monitoring and assessment indicators for the occurrence of macrosomia in GDM pregnancies.