One-hour glucose tolerance test: Improved prediction of diabetes risk

One-hour glucose tolerance test: Improved prediction of diabetes risk | Image Credit: © Minerva Studio - © Minerva Studio - stock.adobe.com.

A 1-hour glucose tolerance test has superiority over a 2-hour test for predicting future diabetes risk, according to a recent study published in Diabetes Care.¹

Low compliance with postpartum glucose testing

New mothers often overlook their own health needs because of the focus they need to place on caring for a baby. This has led to low rates of compliance for postpartum glucose testing among women with gestational diabetes, which has been linked to significantly increased type 2 diabetes risk later in life.¹

“Gestational diabetes provides a unique opportunity to identify a very high risk of a major future illness at a young age,” said Ravi Retnakaran, MD, who is a professor at the University of Toronto’s Temerty Faculty of Medicine. “It is for this reason that, after having gestational diabetes, it is recommended that women do an oral glucose tolerance test within 6 months of delivery.”¹

During pregnancy, the body undergoes increased demands that may highlight limitations in capabilities for producing an adequate amount of insulin to control blood sugar. Postpartum testing is vital for women with gestational diabetes who have a 10-fold increased risk of diabetes later in life, but only half of this population receive postpartum glucose tests.¹

According to Retnakaran, many patients are also unsure which health care providers should order the test. These problems occur in multiple regions worldwide, including Canada, the United States, China, Australia, and across the European Union.¹

A 1-hour oral glucose tolerance test (OGTT) has been recognized by the International Diabetes Federation as a more practical and sensitive option compared to a 2-hour OGTT, which requires overnight fasting followed by taking a sugar drink and waiting an additional 2 hours to undergo an additional blood sugar measurement.¹

Study design and results

With this in mind, investigators conducted the study to compare the efficacy of 1-hour OGTTs and 2-hour OGTTs at 3 months postpartum to predict 5-year diabetes risk.² Two-hour OGTTs were provided to 369 women at 3 months, 1 year, 3 years, and 5 years postpartum.

The change in concordance index (CCI) of Cox proportional hazard regression models was used to assess diabetes prediction from the 3-month OGTT. Of the 70 women diagnosed with diabetes by 2-hour glucose at the 3-month OGTT, the 1-hour glucose test identified 60. Additionally, the 1-hour OGTT identified an additional 96 patients.²

An increase in the cumulative incidence of diabetes was observed over the 5-year period by tertile of 1-hour glucose on the 3-month OGTT. One-hour glucose was reported as the strongest predictor of diabetes during the regression analysis, with a 16.1% change in CCI. This was followed by 2-hour glucose with a 14.9% change in CCI.²

Conclusion

The 1-hour glucose test was also the strongest predictor of future diabetes risk in women with gestational diabetes mellitus, with a rate of 12% This was followed by 2-hour glucose with a rate of 12.8%, indicating the 1-hour OGTT may improve postpartum reclassification following gestational diabetes.²

If you identify an individual who has risk of diabetes, one of the most effective interventions for reducing this risk is helping them to lose weight,” said Retnakaran.¹ “And we are at a point in time where weight loss has never been more achievable for large numbers of people thanks to new medications that are now available.”

References

1. New study suggests a shift in diabetes testing after pregnancy to improve women's health. Lunenfeld-Tanenbaum Research Institute. March 3, 2025. Accessed March 3, 2025. https://www.eurekalert.org/news-releases/1075047?
2. Retnakaran R, Ye C, Kramer CK, et al. One-hour oral glucose tolerance test for the postpartum reclassification of women with hyperglycemia in pregnancy. Diabetes Care. 2025. doi:10.2337/dc24-1848