What are the guidelines for gestational diabetes screening and management?

Gestational Diabetes Screening Guidelines

All pregnant women should be screened for gestational diabetes mellitus (GDM) at 24-28 weeks of gestation using the 50g oral glucose challenge test (OGCT), with high-risk women requiring additional early screening at their first prenatal visit. 1

Risk Assessment

High-Risk Factors (Requiring Early Screening)

• Obesity
• Increased maternal age (>25 years)
• History of previous GDM
• Family history of diabetes (first-degree relative)
• Previous macrosomic infant
• Ethnic groups at increased risk:
  • Hispanic
  • Native American
  • South or East Asian
  • African American
  • Pacific Islander 2, 1

Low-Risk Factors (May Not Require Screening)

• Age <25 years
• Normal pre-pregnancy weight (BMI ≤25 kg/m²)
• No family history of diabetes
• No history of glucose intolerance
• No history of adverse pregnancy outcomes related to GDM
• White race 2

Screening Protocol

Timing

1. High-risk women: Screen at first prenatal visit AND again at 24-28 weeks if initial results are negative 1
2. Average-risk women: Screen at 24-28 weeks 2, 1

Screening Methods

Two approaches are commonly used:

1. Two-Step Approach (Most Common in US)

• Initial screening: 50g OGCT in non-fasting state at 24-28 weeks
• Positive threshold: ≥140 mg/dL (7.77 mmol/L) or alternatively ≥130 mg/dL (7.21 mmol/L)
• Follow-up test: If screening threshold is met, perform 100g OGTT
• Diagnosis: GDM is diagnosed when 2 or more glucose values fall at or above specified thresholds:
  • Fasting: ≥95 mg/dL
  • 1-hour: ≥180 mg/dL
  • 2-hour: ≥155 mg/dL
  • 3-hour: ≥140 mg/dL 2, 1

2. One-Step Approach

• 75g glucose load administered after fasting
• Plasma glucose evaluated at fasting, 1-hour, and 2-hour
• GDM diagnosed if one or more values exceed thresholds:
  • Fasting: ≥92 mg/dL
  • 1-hour: ≥180 mg/dL
  • 2-hour: ≥153 mg/dL 2, 1

Screening Test Performance

• The 50g OGCT with 140 mg/dL threshold has sensitivity of 85% and specificity of 86% 2
• Using a lower threshold of 130 mg/dL increases sensitivity to 99% but reduces specificity to 77% 2
• Evidence suggests the 140 mg/dL threshold provides better balance of sensitivity and specificity 3

Management After Diagnosis

Initial treatment includes:

1. Moderate physical activity
2. Dietary modifications
3. Support from diabetes educators and nutritionists
4. Glucose monitoring

If glucose remains uncontrolled after these interventions:

1. Medication (insulin or oral hypoglycemic agents)
2. Increased surveillance in prenatal care
3. Possible changes in delivery management 2

Postpartum Follow-up

• All women with GDM should be screened for persistent diabetes at 6-12 weeks postpartum 1
• Subsequent screening for diabetes development should occur every 2-3 years 1, 4

Clinical Benefits of Screening and Treatment

Treatment of GDM has been shown to reduce:

• Preeclampsia
• Macrosomia
• Shoulder dystocia 2, 1

Potential Pitfalls

• Missing high-risk women who need early screening
• Improper test preparation affecting OGTT results
• Overlooking postpartum screening
• Assuming normal early screening eliminates the need for 24-28 week testing in high-risk women 1

The evidence supports routine screening after 24 weeks of gestation, with the USPSTF concluding with moderate certainty that there is a moderate net benefit to screening for GDM after 24 weeks to reduce maternal and fetal complications 2.