We devised a complementary quantitative method for gestational diabetes (GDM) that uses the area under the curve (AUC) of the results of the oral glucose tolerance test (OGTT), and evaluated its efficacy in predicting neonates that would be large for gestational age (LGA). The study subjects were 648 pregnant women. The AUC-OGTT (concentration x time) was calculated from the 100-g OGTT results. The incidence of LGA according to each range of the AUC-OGTT was estimated and odds ratios were analyzed using multiple logistic regression analysis.The incidence of LGA increased with the AUC-OGTT value and was 0% for AUC<300, 7.8% for 300-400, 14.9% for 400-500, 20.8% for 500-600, and 45.5% for > or = 600. The odds ratio of LGA increased by approximately two-fold with an increase of 100 in the AUC-OGTT. The results indicated that the AUC-OGTT can be used to quantify the risk of LGA in GDM. The AUC-OGTT could complement a diagnosis of GDM using conventional diagnostic criteria.