What care is recommended for a pregnant woman with a Body Mass Index (BMI) of 24, no history of Gestational Diabetes Mellitus (GDM), and a normal pregnancy?

Routine Gestational Diabetes Screening at 24-28 Weeks

For this asymptomatic pregnant woman with BMI 24 and no history of GDM, perform routine gestational diabetes screening between 24-28 weeks of gestation using either a one-step or two-step approach. 1

Why This Patient Does Not Need Early Screening

This patient does not meet high-risk criteria that would warrant early screening at the first prenatal visit. Early screening (at 12-14 weeks) is specifically reserved for women with: 2, 3, 4

• BMI ≥30 kg/m² (this patient has BMI 24) 2
• History of previous GDM (this patient has none) 2
• First-degree relative with diabetes (not mentioned) 1
• High-risk ethnicity (Hispanic, Native American, South/East Asian, African American, Pacific Islander) 2, 3
• Previous macrosomic infant (>4,500g) 3, 4

Since this patient has a normal BMI (<25 kg/m²) and no stated risk factors, she follows the standard screening timeline. 2

Recommended Screening Approach at 24-28 Weeks

You have two evidence-based options: 1

Two-Step Approach (Most commonly used in US practice)

Step 1: 50g glucose challenge test (non-fasting) 1

• If plasma glucose ≥140 mg/dL at 1 hour, proceed to Step 2 1
• Some guidelines use ≥130 mg/dL threshold for higher sensitivity 1

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

• Diagnosis requires at least 2 of the following values to be met or exceeded: 1
  • Fasting: ≥95 mg/dL
  • 1 hour: ≥180 mg/dL
  • 2 hour: ≥155 mg/dL
  • 3 hour: ≥140 mg/dL

One-Step Approach (International consensus)

75g oral glucose tolerance test (fasting, with measurements at fasting, 1 hour, and 2 hours) 1

• Diagnosis requires only 1 abnormal value: 1
  • Fasting: ≥92 mg/dL
  • 1 hour: ≥180 mg/dL
  • 2 hour: ≥153 mg/dL

Evidence Supporting Universal Screening After 24 Weeks

The USPSTF gives a B recommendation for screening all asymptomatic pregnant women after 24 weeks of gestation, based on moderate net benefit for reducing preeclampsia, macrosomia, and shoulder dystocia. 1 The landmark HAPO study demonstrated that maternal glucose levels at 24-28 weeks show a continuous relationship with adverse outcomes, with no clear threshold for risk. 1

Important: The USPSTF specifically states there is insufficient evidence to recommend screening before 24 weeks in average-risk women. 1

Common Pitfalls to Avoid

• Do not skip screening even in asymptomatic women with normal BMI—universal screening after 24 weeks is recommended for all pregnant women. 1
• Do not perform early screening in this average-risk patient, as it may lead to overdiagnosis without proven benefit. 5
• Do not use HbA1c alone for GDM diagnosis during pregnancy—oral glucose tolerance testing is the standard. 3, 4

If GDM Is Diagnosed

• Initiate nutritional counseling and glucose self-monitoring immediately 3, 4, 6
• Target fasting glucose <95 mg/dL and 1-hour postprandial <140 mg/dL 3, 4
• Start insulin therapy if lifestyle modifications fail to achieve targets 3, 4, 6
• Screen for persistent diabetes 4-12 weeks postpartum with 75g OGTT 1, 3, 4
• Continue lifelong screening every 2-3 years thereafter 1, 4