From the Guidelines
The diagnosis of gestational diabetes is made when one or more values are met or exceeded during a 75g oral glucose tolerance test (OGTT), with thresholds of fasting plasma glucose ≥5.1 mmol/L, 1-hour postprandial glucose ≥10.0 mmol/L, or 2-hour postprandial glucose ≥8.5 mmol/L, as established by the most recent guidelines 1. The thresholds for the 1-hour and 2-hour postprandial glucose levels are 10.0 mmol/L and 8.5 mmol/L, respectively, according to the 2024 standards of care in diabetes 1. Key points to consider when diagnosing gestational diabetes include:
- The test should be performed between 24-28 weeks of gestation in women not previously diagnosed with diabetes.
- Women with risk factors may be screened earlier.
- Only one abnormal value is needed for diagnosis.
- These criteria were established based on the association between maternal hyperglycemia and increased risks of adverse pregnancy outcomes, including macrosomia, neonatal hypoglycemia, and cesarean delivery, as demonstrated by the HAPO study, although the exact details of the HAPO study are not provided in the given evidence 1. It's essential to note that these thresholds are lower than those used for diagnosing diabetes in non-pregnant individuals because pregnancy naturally induces some insulin resistance, and even modest elevations in blood glucose during pregnancy can lead to adverse outcomes.
From the Research
Thresholds for Glucose Tolerance Test
The thresholds for the 75-g 2-hour oral glucose tolerance test (OGTT) that confer a diagnosis of gestational diabetes are:
- Fasting plasma glucose ≥ 5.1 mmol/L (92 mg/dL)
- 1-hour plasma glucose ≥ 10 mmol/L (180 mg/dL)
- 2-hour plasma glucose ≥ 8.5 mmol/L (153 mg/dL) 2 Alternatively, other studies suggest the following thresholds:
- Fasting plasma glucose ≥ 5.4 mmol/L (97 mg/dL)
- 1-hour plasma glucose ≥ 10.5 mmol/L (189 mg/dL)
- 2-hour plasma glucose ≥ 8.4 mmol/L (151 mg/dL) 3
Comparison of Thresholds
Different studies propose slightly different thresholds for the diagnosis of gestational diabetes using the 75-g 2-hour OGTT. However, the most commonly cited thresholds are those proposed by the International Association of Diabetes in Pregnancy Study Groups (IADPSG) 2.
Diagnosis of Gestational Diabetes
The diagnosis of gestational diabetes is typically made based on the results of a 75-g 2-hour OGTT, with one or more elevated plasma glucose values 2, 4. The specific thresholds used to diagnose gestational diabetes may vary depending on the guidelines or criteria being followed.