Gestational Diabetes Mellitus (GDM): Diagnostic Criteria and Screening Methods

Introduction

Gestational Diabetes Mellitus (GDM) is defined as glucose intolerance of varying degrees that begins or is first recognized during pregnancy. It poses significant risks to both maternal and fetal health if not properly managed.

Importance of Screening

Early detection and management of GDM are crucial to prevent adverse perinatal outcomes. Screening allows timely intervention and supports glycemic control through lifestyle modification or pharmacotherapy.

Diagnostic Criteria

One-Step Approach

• A 75-gram oral glucose tolerance test (OGTT) is performed at 24–28 weeks gestation.
• Diagnostic thresholds (based on IADPSG):
  - Fasting plasma glucose ≥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)
• Diagnosis is confirmed if any one of the thresholds is met or exceeded.

Two-Step Approach

• Step 1: 50-gram glucose challenge test (non-fasting)
  • Plasma glucose measured after 1 hour
  • If ≥130–140 mg/dL, proceed to OGTT
• Step 2: 100-gram OGTT (fasting)
  • Diagnosis requires ≥2 abnormal values based on Carpenter and Coustan criteria:
  • Fasting: ≥95 mg/dL
  • 1-hour: ≥180 mg/dL
  • 2-hour: ≥155 mg/dL
  • 3-hour: ≥140 mg/dL

Risk Factors

• Obesity
• Advanced maternal age
• Family history of diabetes
• Previous GDM or macrosomic infant

Conclusion

Proper screening and adherence to diagnostic protocols are essential for early identification and management of GDM. Patient education and interdisciplinary care significantly improve maternal and fetal outcomes.