From the Guidelines
There is no specific value at which a pregnant person auto-fails the glucose tolerance screen and is diagnosed on the spot, as the diagnosis of gestational diabetes mellitus (GDM) typically requires a two-step process or meeting specific criteria during the oral glucose tolerance test (OGTT). The initial glucose load test (GLT) with a 50-g glucose dose is used as a screening tool, and if the plasma glucose level measured 1 hour after the load is ≥130,135, or 140 mg/dL, the individual proceeds to a 100-g OGTT 1. The diagnosis of GDM is made when at least two of the following four plasma glucose levels (measured fasting and at 1,2, and 3 hours during OGTT) are met or exceeded:
- Fasting: 95 mg/dL
- 1 hour: 180 mg/dL
- 2 hours: 155 mg/dL
- 3 hours: 140 mg/dL According to the American College of Obstetricians and Gynecologists (ACOG), any of the commonly used thresholds of 130,135, or 140 mg/dL for the 1-hour 50-g GLT can be used, but one elevated value is not sufficient for an immediate diagnosis 1. Key points to consider in the diagnosis and management of GDM include:
- The two-step strategy for diagnosing GDM, which includes the initial GLT and the subsequent OGTT if the GLT is abnormal
- The criteria for diagnosing GDM based on the OGTT results
- The importance of prompt initiation of treatment and management strategies to reduce risks to both mother and baby.
From the Research
Glucose Tolerance Screen Threshold
- The provided studies do not specify a certain value at which a pregnant person auto-fails the glucose tolerance screen and is diagnosed on the spot 2, 3, 4, 5, 6.
- However, the studies discuss the diagnostic criteria and approaches for gestational diabetes mellitus (GDM), including the use of a 75-g oral glucose tolerance test (OGTT) and the measurement of fasting plasma glucose (FPG) and 2-hour plasma glucose (PG) levels 2, 5.
- One study found that a fasting glucose level of ≤5.2 mmol/L at OGTT was associated with a high probability of response to metformin treatment in women with GDM 5.
- Another study reported that women with GDM who required insulin treatment had higher FPG and PG levels compared to those who responded to metformin or diet-only treatment 3.
Diagnostic Approaches
- The studies discuss the use of a two-step approach (1-hour 50-g glucose challenge test followed by 3-hour 100-g OGTT) and a one-step approach (75-g OGTT) for GDM screening and diagnosis 2.
- The one-step approach has been recommended as an option for GDM diagnosis since 2010, but its clinical benefit in reducing adverse pregnancy outcomes remains controversial 2.
- The choice of diagnostic approach may depend on various factors, including the population being screened and the availability of resources 2, 4.