75g oral glucose tolerance test (OGTT) values — enter what's available.
How it's calculated
Under the IADPSG/WHO one-step approach, gestational diabetes is diagnosed if the value at any single timepoint of a 75g OGTT meets or exceeds its threshold — no second confirmatory test is required.
Diagnostic thresholds
| Timepoint | Threshold |
|---|---|
| Fasting | ≥92 mg/dL (5.1 mmol/L) |
| 1-hour | ≥180 mg/dL (10.0 mmol/L) |
| 2-hour | ≥153 mg/dL (8.5 mmol/L) |
Clinical use
- Typically performed at 24-28 weeks' gestation in women without a prior diabetes diagnosis, or earlier in those with risk factors.
- Some regions instead use a two-step approach (a 50g glucose challenge test screen, followed by a 100g OGTT with Carpenter-Coustan criteria if positive) — this calculator applies the one-step IADPSG/WHO criteria, the more widely adopted global standard.
- A positive result should prompt initiation of dietary counselling, glucose monitoring, and obstetric follow-up per local protocol.
Frequently asked questions
How many abnormal OGTT values are needed to diagnose GDM?
Under IADPSG/WHO one-step criteria, just one abnormal value (fasting, 1-hour, or 2-hour) meeting or exceeding its threshold is sufficient to diagnose gestational diabetes.
What's the difference between the one-step and two-step approach?
The one-step approach (used here) is a single 75g OGTT with IADPSG/WHO thresholds. The two-step approach first uses a 50g glucose challenge test as a screen, then a confirmatory 100g OGTT with Carpenter-Coustan criteria only if the screen is positive. Both are used internationally; check local/institutional protocol.
When is GDM screening usually done?
Typically at 24-28 weeks' gestation for most pregnant women, though those with risk factors (e.g. obesity, prior GDM, strong family history) are often screened earlier as well.
References
- International Association of Diabetes and Pregnancy Study Groups (IADPSG) Consensus Panel. Recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care. 2010;33:676-682.
- World Health Organization. Diagnostic Criteria and Classification of Hyperglycaemia First Detected in Pregnancy. 2013.