A Korean multicenter study of prenatal risk factors for overt diabetes during the postpartum period after gestational diabetes mellitus

Objective To identify prenatal risk factors for postpartum diabetes among pregnant women with gestational diabetes mellitus (GDM). Methods In a retrospective study, baseline characteristics and data from a postpartum 75-g glucose tolerance test (GTT) were reviewed for patients with GDM who had delivered in four Korean tertiary institutions from 2006 to 2012. Clinical characteristics were compared between women with and those without postpartum diabetes. Cutoffs to predict postpartum diabetes and diagnostic values were calculated from receiver operating characteristic (ROC) curves. Results Of 1637 patients with GDM, 498 (30.4%) underwent a postpartum 75-g GTT. Postpartum diabetes was diagnosed in 40 (8.0%) patients and impaired glucose intolerance in 157 (31.5%). Women with postpartum diabetes had higher glycated hemoglobin (HbA_1c) levels at GDM diagnosis (P = 0.008) and higher 100-g GTT values (P < 0.05 for all). In ROC curve analysis, optimal cutoffs for predicting postpartum diabetes were 0.058 for HbA_1c level and 5.3 mmol/L (fasting), 10.9 mmol/L (1 h), 10.2 mmol/L (2 h), and 8.6 mmol/L (3 h) for 100-g GTT. The highest sensitivity was observed for 3-h 100-g GTT (76.9%) and the highest positive predictive value was for HbA_1c at diagnosis (15.2%). Conclusion HbA_1c level at GDM diagnosis and 100-g GTT values could be used to identify patients at high risk of postpartum diabetes who should undergo postpartum screening.