What are the American College of Obstetricians and Gynecologists (ACOG) guidelines for the 1-hour glucose challenge test (GCT) in early pregnancy?

ACOG Guidelines on Early 1-Hour Glucose Challenge Test (GCT)

According to the American College of Obstetricians and Gynecologists (ACOG), individuals with clinical characteristics consistent with high risk for gestational diabetes mellitus (GDM) should undergo glucose testing as early as possible in pregnancy, rather than waiting for the standard 24-28 week screening window. 1

High-Risk Individuals Requiring Early Screening

Early screening is recommended for women with:

• Marked obesity 1
• Personal history of GDM 1
• Glycosuria 1
• Strong family history of diabetes 1
• Member of high-risk ethnic population (e.g., African-American, Latino, Native American, Asian-American, Pacific Islander) 1

Early Screening Protocol

For high-risk women, ACOG recommends:

• Testing should be performed as soon as possible after the first prenatal visit 1
• The same screening methods used at 24-28 weeks can be applied for early screening 1
• If early screening is negative, these high-risk women should be retested at 24-28 weeks 1

Standard GDM Screening Options (24-28 weeks)

ACOG endorses two approaches for GDM screening at 24-28 weeks:

Two-Step Approach (ACOG Preferred)

1. Step 1: 50g glucose load test (GLT), non-fasting, with plasma glucose measurement at 1 hour 1

   • If glucose ≥130,135, or 140 mg/dL (7.2,7.5, or 7.8 mmol/L), proceed to step 2 1
   • ACOG accepts any of these three thresholds 1

2. Step 2: 100g oral glucose tolerance test (OGTT), fasting 1

   • Diagnosis made when at least one (per ACOG's updated recommendation) of the following values is met or exceeded (Carpenter-Coustan criteria) 1:
     • Fasting: 95 mg/dL (5.3 mmol/L)
     • 1h: 180 mg/dL (10.0 mmol/L)
     • 2h: 155 mg/dL (8.6 mmol/L)
     • 3h: 140 mg/dL (7.8 mmol/L)

One-Step Approach (Alternative)

• 75g OGTT, fasting, with measurements at fasting, 1h, and 2h 1
• Diagnosis made when any of these values is met or exceeded:
  • Fasting: 92 mg/dL (5.1 mmol/L)
  • 1h: 180 mg/dL (10.0 mmol/L)
  • 2h: 153 mg/dL (8.5 mmol/L)

Diagnostic Criteria for Overt Diabetes in Early Pregnancy

For diagnosing overt diabetes (not GDM) in early pregnancy, any of these criteria can be used 2:

• Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L)
• 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during OGTT
• Random plasma glucose ≥200 mg/dL (11.1 mmol/L) with symptoms of hyperglycemia

Clinical Considerations

• The two-step approach identifies fewer women with GDM (5-6%) compared to the one-step approach (15-20%) 1
• The increased diagnosis rate with the one-step approach raises concerns about medicalization of pregnancy and healthcare costs 1, 3
• However, women diagnosed by the one-step approach show 3.4-fold higher risk of developing prediabetes and type 2 diabetes later in life 1
• ACOG continues to recommend the two-step approach despite international movement toward the one-step approach 1
• Early screening in high-risk populations improves detection of pre-existing diabetes that was previously undiagnosed 4

Common Pitfalls to Avoid

• Failing to repeat abnormal test results for confirmation 2
• Using GDM diagnostic thresholds for diagnosing overt diabetes 2
• Relying solely on random glucose measurements without confirmatory testing 2
• Not retesting high-risk women at 24-28 weeks if early screening was negative 1
• Overlooking risk factors that warrant early screening 4