Insulin Resistance in GDM A1 vs Healthy Pregnancy: A Comparative Study Using METS-IR and TyG Index.

Purpose: To compare the whole-pregnancy insulin resistance level between women with gestational diabetes mellitus A1 (GDM A1) and healthy pregnant women by means of the METS-IR and the TyG index, and to assess the impact of such resistance on pregnancy outcomes. Methods: 344 parturients were classified as GDM A1 (n=118) or normal by 75-g oral glucose tolerance test (OGTT) conducted at 24-28 weeks of gestation. Body mass index (BMI), fasting plasma glucose, triglycerides, and high-density lipoprotein cholesterol were measured in early, mid-, and late pregnancy to calculate METS-IR and TyG index values for each period. Longitudinal changes and early-pregnancy values of METS-IR and TyG were compared between groups and related to obstetric outcomes. Furthermore, mediation analysis was conducted to assess the mediating effect of BMI gain on the relationship between TyG index and METS-IR during pregnancy. Results: METS-IR indicated that insulin resistance in mid- and late pregnancy was significantly higher in the GDM A1 group than in the control group, while the TyG index showed a similar trend beginning in early pregnancy. However, the magnitude of increase in insulin resistance from early to mid-pregnancy did not differ significantly between the two groups. From mid- to late pregnancy, METS-IR increased more rapidly in the control group than in the GDM A1 group, whereas no significant difference was observed in TyG index changes. Early-pregnancy METS-IR and TyG values were not significantly associated with mode of delivery, neonatal birth weight, or placental weight. Mediation analysis revealed that BMI gain had a significantly greater mediating effect on METS-IR elevation than on TyG increase. Conclusion: Women with GDM A1 exhibited higher insulin resistance throughout pregnancy compared to healthy controls. Early-pregnancy METS-IR and TyG indices were associated with GDM A1 diagnosis but not with delivery characteristics or fetal parameters. Due to the influence of BMI changes during pregnancy, METS-IR may not be a reliable surrogate marker of insulin resistance in this population.