1-hour Oral Glucose Tolerance Test for the Postpartum Reclassification of Women with Hyperglycemia in Pregnancy

OBJECTIVE: The International Diabetes Federation recently endorsed a 1-hour oral glucose tolerance test (OGTT) as more convenient than the conventional 2-hour OGTT. In practice, women with hyperglycemia in pregnancy are advised to undergo a 2-hour OGTT within 6-months after delivery but this test is often not completed, partly owing to its inconvenience for busy mothers. Recognizing the potential advantage of the 1-hour OGTT in this setting, we sought to compare 1-hour and 2-hour OGTT glucose measurements at 3-months postpartum as predictors of dysglycemia (pre-diabetes/diabetes) over the first 5-years postpartum. RESEARCH DESIGN AND METHODS: Three-hundred-and-sixty-nine women across a range of glucose tolerance in pregnancy (from normoglycemia to gestational diabetes (GDM)) underwent multi-sample 2-hour 75g OGTTs at 3-months, 1-year, 3-years and 5-years postpartum. Glucose measurements from the 3-month OGTT were ranked as predictors of dysglycemia (both criteria) by change in concordance index (CCI) of Cox proportional hazard regression models. RESULTS: At the 3-month OGTT, 1-hour glucose identified all but 10 of 70 women concurrently diagnosed with dysglycemia by 2-hour glucose, while diagnosing an additional 96 women. The cumulative incidence of dysglycemia progressively increased over 5-years by tertile of 1-hour glucose on the 3-month OGTT (p<0.0001). On regression analyses, the strongest predictor of dysglycemia was 1-hour glucose (change in CCI: 16.1%), followed by 2-hour glucose (14.9%). In women with GDM, 1-hour glucose again emerged as strongest predictor of dysglycemia (13.0%), followed by 2-hour glucose (12.8%). CONCLUSION: The 1-hour OGTT may offer a strategy for increasing rates of postpartum reclassification following hyperglycemia in pregnancy.