(1107) Disposition Index Better Differentiates Insulin Dynamics in Gestational Diabetes Than Matsuda or Insulinogenic Index

To examine whether the disposition index (DI), which reflects the relationship between insulin sensitivity and secretion, better characterizes underlying insulin dynamics in women with GDM compared to the Matsuda index (MI) or insulinogenic index (IGI), with the goal of developing physiologically relevant subclassifications of GDM beyond glucose-based diagnosis alone.


Study Design:

This was a cross-sectional study of 488 pregnant women who underwent a 75g oral glucose tolerance test (OGTT) between 24 and 32 weeks of gestation at a tertiary perinatal center in Japan. Based on OGTT results, women were categorized as having GDM (n=174) or normal glucose tolerance (n=314). Three indices were calculated from the OGTT data: MI (whole-body insulin sensitivity), IGI (early-phase insulin secretion), and DI (IGI × MI, reflecting β-cell compensatory capacity). We compared means between groups using t-tests and evaluated discriminatory ability with ROC curve analysis. The area under the curve (AUC) was compared for each index.


Results:

All three indices were significantly lower in the GDM group compared to the normal group (p< 0.00001 for each). Disposition index demonstrated the highest discriminatory ability for identifying GDM: AUC for DI = 0.80, compared to IGI = 0.68 and MI = 0.62 (Figure). These results confirm that DI, which integrates both insulin sensitivity and secretion, more accurately captures the pathophysiologic basis of GDM than either index alone.


Conclusion:

Although GDM is currently diagnosed based solely on maternal glucose levels, this study highlights the potential of disposition index as a tool for pathophysiologic subclassification. DI may better reflect the balance between insulin sensitivity and secretion in GDM, which could have implications for predicting perinatal outcomes or guiding individualized care.