Screening and Diagnosing Diabetes Mellitus During Pregnancy: Revised Criteria

by Dr. Jessica Trusler, Dr. Marietjie Meyer, Dr. Carolyn Fedler & Dr. Marita du Plessis

PATHCHAT Edition No. 15
Please contact your local Ampath pathologist for more information.

Why Revise the Gestational Diabetes Mellitus (GDM) Criteria?

🔹 Previous Definition of GDM:

• Any degree of hyperglycaemia during pregnancy, including:
  • Overt diabetes mellitus (DM).
  • Impaired glucose tolerance (IGT).
  • Impaired fasting glycaemia (IFG) (as defined in non-pregnant adults).
• Focus had been on the future maternal risk of diabetes rather than immediate pregnancy outcomes.

🔹 New Research Findings – HAPO Study (2008):

• Confirmed a continuous increase in adverse pregnancy outcomes with increasing glucose levels.
• Led to re-evaluation of screening & diagnosis criteria by two major consensus groups:
  • International Association of Diabetes and Pregnancy Study Group (IADPSG).
  • American Diabetes Association (ADA).

🔹 Changes in the New Guidelines (IADPSG/ADA):

• Lower fasting & two-hour plasma glucose thresholds.
• Diagnosis requires only ONE abnormal value on a 75 g Oral Glucose Tolerance Test (OGTT).
• Universal screening recommended at 24–28 weeks’ gestation.

🔹 Challenges & Controversies:

• Global increase in obesity & Type 2 DM → More GDM cases detected with new criteria.
• Increased financial burden of universal screening programs.

📌 Current South African Recommendation:

• Follow the WHO (2013) guidelines until an official South African guideline is published.

WHO 2013 Recommendations for Diagnosing Diabetes in Pregnancy

1. Classification of Hyperglycaemia in Pregnancy

🔹 Two main categories:

• Diabetes in Pregnancy → Criteria same as overt diabetes.
• Gestational Diabetes Mellitus (GDM) → Milder hyperglycaemia specific to pregnancy.

2. Criteria for Diagnosing Diabetes in Pregnancy

✅ Diabetes in pregnancy is diagnosed if ANY of the following criteria are met:

• Fasting plasma glucose ≥ 7.0 mmol/L.
• Two-hour plasma glucose ≥ 11.1 mmol/L (after 75 g OGTT).
• Random plasma glucose ≥ 11.1 mmol/L + diabetes symptoms.
• Abnormal test results should be confirmed on another day or with another test.

3. Criteria for Diagnosing GDM

✅ GDM is diagnosed at any time during pregnancy if ANY of the following criteria are met:

• Fasting plasma glucose: 5.1 – 6.9 mmol/L.
• One-hour plasma glucose: ≥ 10.0 mmol/L (after 75 g OGTT).
• Two-hour plasma glucose: 8.5 – 11.0 mmol/L (after 75 g OGTT).

📌 Note:

• The 50 g and 100 g OGTT tests are no longer recommended – only the 75 g OGTT is used.
• Criteria are based on the risk of adverse perinatal outcomes.

Guidelines for Conducting the 75 g OGTT

✅ To ensure accurate test results, the following conditions must be met:

• Consume at least 150 g of carbohydrates daily for 3 days before the test.
• Fast for 10–16 hours before the test.
• The test must be conducted between 07:00 and 09:00 AM.

Use of HbA1c in Pregnancy

📌 Currently, HbA1c levels are NOT recommended for diagnosing diabetes in pregnancy.

• The optimal HbA1c cut-off values for diagnosing GDM remain unestablished.

Key Takeaways for Healthcare Providers

✅ Gestational diabetes screening & diagnosis criteria have been revised to improve pregnancy outcomes.
✅ New WHO guidelines (2013) should be followed in South Africa until local guidelines are established.
✅ The 75 g OGTT is now the only recommended test for diagnosing GDM.
✅ Diagnosis requires only one abnormal glucose value.
✅ HbA1c is not yet a reliable diagnostic tool for GDM.

References

1. American Diabetes Association. (2010). Diagnosis and classification of diabetes mellitus. Diabetes Care, 33(Suppl. 1): S62–S69.
2. HAPO Study Cooperative Research Group. (2008). Hyperglycemia and adverse pregnancy outcomes. N Engl J Med, 358:1991–2002.
3. International Association of Diabetes and Pregnancy Study Groups Consensus Panel. (2010). Recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care, 33(3): 676–682.
4. World Health Organization. (2006). Definition and diagnosis of diabetes mellitus and intermediate hyperglycemia: Report of a WHO/IDF Consultation. Geneva: WHO.
5. World Health Organization. (2013). WHO/NMH/MND/13.2.