Gestational Diabetes

ADA criteria for gestational diabetes mellitus (GDM

The American Diabetes Association (ADA) in their 2025 “Standards of Care in Diabetes” maintains support for the two-step approach to screening for gestational diabetes mellitus (GDM)—that is, beginning with a 50 g nonfasting glucose challenge test (GCT), followed, if abnormal, by a diagnostic 100 g, 3-hour oral glucose tolerance test (OGTT) using Carpenter & Coustan criteria. This remains the ADA’s preferred process.

ADA (2025) Screening Recommendation for GDM

  • Preferred approach: Two-step method
    1. First step: 50 g nonfasting glucose challenge test (GCT), typically conducted at 24–28 weeks of gestation.
    2. Second step (if GCT abnormal): 100 g, 3‑hour OGTT, using Carpenter & Coustan thresholds (not the older NDDG criteria), as it increases sensitivity and avoids missing treatable GDM. Diabetes.org+2ADA Meeting News+2The ObG Project
  • Fastidious diagnostic criteria: ADA favours Carpenter & Coustan over NDDG thresholds, emphasizing that the latter may miss opportunities to diagnose and manage GDM effectively. wafp.org+4The ObG Project+4Diabetes.org+4
  • Timing: Routine screening occurs between 24–28 weeks gestation, with early screening considered for those with risk factors—but routine early testing is not recommended. The ObG Project

he one-step 75 g OGTT (IADPSG/WHO) is used in some countries and can detect a higher prevalence of GDM—but the ADA continues to prefer the two-step method due to concerns about overdiagnosis and lack of definitive evidence showing superior outcomes with the one-step approach. While some studies support the one-step method, the ADA hasn’t shifted away from the two-step strategy as of 2025. The ObG Project+1

Specific Carpenter & Coustan (C&C) thresholds for the 100 g, 3-hour OGTT used in diagnosing gestational diabetes (per ADA/ACOG recommendations).

Carpenter & Coustan Threshold Values (100 g, 3-hour OGTT)

A diagnosis of gestational diabetes requires two or more of the following plasma glucose values to meet or exceed these thresholds:

Quick Reference Table

Time Point

Carpenter & Coustan Threshold

Fasting

≥ 95 mg/dL

1-hour

≥ 180 mg/dL

2-hour

≥ 155 mg/dL

3-hour

≥ 140 mg/dL

Meeting or exceeding two or more of these values is diagnostic for gestational diabetes.

Why These Thresholds?

Carpenter & Coustan thresholds are lower across all time points compared to the older National Diabetes Data Group (NDDG) criteria, which are as follows:

Because the C&C thresholds are “more inclusive,” studies show they diagnose approximately 30–50% more GDM cases compared to NDDG criteria. academics.prismahealth.org+6PMC+6PMC+6

Summary

  • The ADA and ACOG (2025) favor the two-step approach, using the 100 g, 3-hour OGTT with Carpenter & Coustan thresholds as outlined above.
  • Diagnosis requires two or more elevated glucose measurements at or above the Carpenter & Coustan cutoffs.

WHO criteria for gestational diabetes mellitus (GDM)

World Health Organization (WHO) recommendation on using the 75 g OGTT for diagnosing gestational diabetes mellitus (GDM):

  • In 2013, the WHO adopted the diagnostic criteria developed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) for use with a 75 g oral glucose tolerance test (OGTT). According to these criteria, GDM is diagnosed if at least one of the following plasma glucose values is met or exceeded:

Additionally, WHO classifies overt diabetes in pregnancy (DIP) if:

For a consolidated documentation of these thresholds under global guidelines (WHO, FIGO, IADPSG), see:

  • The WHO guideline titled “Diabetes Mellitus and Pregnancy” (2018), which provides a table of OGTT cut‑offs. It specifies:

Summary of WHO-Recommended 75 g OGTT Criteria

Category

Fasting (FPG)

1-Hour

2-Hour

GDM (IADPSG / WHO)

≥ 5.1 mmol/L (92 mg/dL)

≥ 10.0 mmol/L (180 mg/dL)

≥ 8.6 mmol/L (153 mg/dL)

Overt Diabetes (DIP)

≥ 7.0 mmol/L (126 mg/dL)

—

≥ 11.1 mmol/L (200 mg/dL)

Prevalence of Gestational Diabetes

Prevalence by Region, Stratified by OGTT Strategy

United States

Europe

  • Classic pooled prevalence: around 10–11% (wide range, reflecting variation across countries and methods) MDPI+4Oxford Academic+4BioMed Central+4.
  • Some studies report parts of Europe exceeding 20%, especially where one‑step OGTT is used or in high‑risk populations PMC+1.

India

  • One meta‑analysis (2024) pooled across many studies reports overall GDM prevalence at ~13%, with regional variation:
  • A specific study (2024) reported prevalence by OGTT at 19.2% in India, compared with 14.5% in the UK The Lancet—suggesting either a high-risk population or use of one-step OGTT criteria.
  • Overall, these figures reflect strong regional heterogeneity and diagnostic differences.

Summary Table

Region

Two-Step OGTT Prevalence

One-Step OGTT Prevalence

USA

~5.2%

~13.7% to ~17.8%

Europe

~10–11% (wide range)

Often higher, up to >20% in some areas

India

~7–16% (varies by region)

As high as ~19.2% in some settings

Why the Big Spread?

  • Methodology matters: One-step OGTT captures more cases by design.
  • Population risk differences: Maternal age, obesity, socioeconomic factors, and ethnicity play big roles.
  • Variability in adoption of guidelines: Different countries and even regions within countries may follow different diagnostic thresholds or timing for testing.

 

 

Test for Gestational Diabetes in the Maternity Record (WHO)

Test for Gestational Diabetes in the Maternity Record

In Germany, gestational diabetes, with a prevalence of slightly under 10%, is one of the most common pregnancy complications. In many cases, it is diagnosed too late or not at all.

In Germany the test should be performed for every pregnant woman between the 24th and 28th week of gestation.
For high-risk patients, it should be performed before the 24th week. High-risk patients include:

  • Women over 45 years of age
  • Women with a BMI over 30 kg/m²
  • Women with parents or siblings who have diabetes
  • Women who have previously given birth to a child weighing over 4500 g
  • Women with hypertension or a history of borderline elevated blood sugar levels
  • Women with vascular diseases such as coronary heart disease, peripheral artery disease, or other circulatory disorders

These high-risk patients should be screened before the 24th week of gestation.

According to the new guidelines, the diagnosis must be based on venous plasma glucose measurements using a quality-controlled method.
Measuring capillary blood from a finger prick using a test-strip meter is no longer acceptable due to lack of accuracy.

How is the Gestational Diabetes Test Conducted?

In Germany the One‑step 75 g OGT is recommended .

For a valid oral glucose tolerance test (OGTT), the following conditions must be met:

  • Performed in the morning
  • At least 8 hours of fasting beforehand
  • No restriction of carbohydrate intake for at least three days before the test
  • Drink 75 g of glucose dissolved in 300 ml of water within 3–5 minutes
  • The pregnant woman should remain seated in the clinic during the test
  • Blood glucose must be measured using a quality-controlled method
  • Self-monitoring devices are not suitable

The test involves a fasting patient drinking 75 g of glucose in 200 ml of water in the morning. Blood glucose is measured before drinking, then at 1 hour and 2 hours afterward — all from venous samples, typically taken via a plastic cannula.

When is Gestational Diabetes Diagnosed?

Gestational diabetes is diagnosed if at least one of the three values exceeds the limit WHO Criteria:

  • Fasting: ≥ 92 mg/dl (5.1 mmol/l)
  • 1 hour after: ≥ 180 mg/dl (10 mmol/l)
  • 2 hours after: ≥ 153 mg/dl (8.5 mmol/l)

If the fasting value is ≥ 126 mg/dl (7 mmol/l), it is not gestational diabetes but newly developed diabetes during pregnancy.

Increased Risk for Mother and Child

For the unborn child, gestational diabetes significantly increases the risk of:

  • High birth weight
  • Preterm birth
  • Caesarean delivery
  • Birth injuries such as shoulder dystocia
  • Hyperbilirubinemia requiring intensive care
  • Neonatal hypoglycemia, which can lead to permanent brain damage

Mothers have a higher risk for preeclampsia and, in the long term, a ~50% higher risk of developing type 2 diabetes.

Treatment of Gestational Diabetes

After diagnosis, treatment should begin immediately in a specialized diabetes center or clinic.
The first step is an individual nutrition plan and training in self-monitoring of blood glucose.

If values remain outside the target range despite diet and lifestyle adjustments, insulin therapy is necessary. Oral medications are not permitted during pregnancy.

Blood Glucose Targets

  • Fasting & pre-meal: 65–95 mg/dl (3.6–5.3 mmol/l)
  • 1 hour post-meal: < 140 mg/dl (7.7 mmol/l)
  • 2 hours post-meal: < 120 mg/dl (6.6 mmol/l)

Targets may be adapted individually based on ultrasound measurements of the baby’s abdominal circumference:

  • < 10th percentile: Fasting < 105 mg/dl, 1-hour post-meal < 160 mg/dl
  • 10–75th percentile: Standard targets above
  • 75th percentile: Fasting < 85 mg/dl, 1-hour post-meal < 120 mg/dl

Insulin is Safe in Pregnancy

Insulin does not cross the placenta and effectively reduces glucose load to the fetus.
Commonly used: Regular insulin and NPH insulin; short-acting analogs (Aspart, Lispro) in some cases; long-acting analogs (Lantus, Levemir) are not recommended.

Cooperation Between Doctors

Close coordination between diabetologist and gynecologist is essential to balance blood sugar control with fetal growth monitoring.

Weight Management During Pregnancy

Weight loss is to be avoided. Recommended weight gain depends on pre-pregnancy BMI:

  • BMI ≤ 18.5: 12.5–18 kg
  • Normal BMI: 11.5–16 kg
  • Overweight (BMI 25–29.9): 7–11.5 kg
  • Obese (BMI ≥ 30): 5–9 kg

After Delivery

A follow-up OGTT is recommended 6–12 weeks postpartum.
A scoring system developed at Helmholtz Zentrum München can predict future type 2 diabetes risk:

Score formula:
5 × BMI (early pregnancy) + 132 (if treated with insulin) + 44 (if family history present) − 35 (if breastfed)

Risk categories:

  • ≤ 140 → ~11% risk within 5 years
  • 141–220 → ~29% risk
  • 221–300 → ~64% risk
  • 300 → ~80% risk

References:

WHO Guideline: Diabetes Mellitus and Pregnancy (2018)

The American Diabetes Association (ADA)  2025 “Standards of Care in Diabetes” Diabetes Care December 2024, Vol.48, S14-S26. doi:https://doi.org/10.2337/dc25-S001