Abnormal Thresholds for Nonfasting 1-Hour 50-g Glucose Challenge Test in GDM Screening

Introduction to GDM Screening

The American College of Obstetricians and Gynecologists (ACOG) recommends a threshold of ≥140 mg/dL for the nonfasting 1-hour 50-g glucose challenge test (GCT), though thresholds of 130 mg/dL or 135 mg/dL are also acceptable, particularly in high-risk populations 1

The two-step approach begins with a 50-g glucose load test (GLT) performed in a nonfasting state at 24-28 weeks gestation 2, 3, 4
If the plasma glucose level measured 1 hour after the load is ≥140 mg/dL, the patient proceeds to a 100-g OGTT 2, 1
The 2024 American Diabetes Association guidelines specifically note that thresholds of 130, 135, or 140 mg/dL are all acceptable for the first step of the two-step approach 1
The threshold of 140 mg/dL identifies approximately 80% of women with GDM, while using a lower cutoff of 130 mg/dL increases the yield to about 90% 5

ACOG specifically recommends a lower threshold of 135 mg/dL in high-risk ethnic minorities with higher prevalence of GDM 2
Some experts recommend using 130 mg/dL as the threshold for certain populations 2, 5

After a positive GCT result, a diagnostic 100-g OGTT should be performed in the fasting state 2, 4, 1
The diagnosis of GDM is made when at least two of the following four plasma glucose levels are met or exceeded:
- Fasting: 95 mg/dL 5
- 1-hour: 180 mg/dL 5
- 2-hour: 155 mg/dL 5
- 3-hour: 140 mg/dL 2, 4, 1

Using different thresholds without considering the population's risk profile may lead to under or over-diagnosis 2, 1
Failure to follow up positive screening results with the diagnostic OGTT may lead to missed diagnoses 2, 1