What is the evaluation and treatment approach for gestational diabetes?

Evaluation and Treatment of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) should be managed with medical nutrition therapy and physical activity as first-line treatment, with insulin added when lifestyle modifications fail to achieve glycemic targets. 1, 2

Diagnosis and Screening

Screening Approach

• Universal screening at 24-28 weeks gestation using either:
  • One-step approach: 75g oral glucose tolerance test (OGTT) 1
  • Two-step approach: 50g glucose challenge test followed by 100g OGTT if positive 1

Diagnostic Criteria

• Using 75g OGTT, GDM is diagnosed if one or more values meet or exceed:
  • Fasting: ≥92 mg/dL (5.3 mmol/L)
  • 1-hour: ≥180 mg/dL (10.0 mmol/L)
  • 2-hour: ≥153 mg/dL (8.6 mmol/L) 1, 3

Early Screening

• Screen high-risk women at first prenatal visit:
  • History of GDM
  • Marked obesity
  • Strong family history of diabetes
  • Previous macrosomic infant
  • Glycosuria 1

Treatment Algorithm

Step 1: Lifestyle Modifications

• Medical nutrition therapy (MNT) is the cornerstone of GDM treatment 1

  • Individualized plan developed with registered dietitian
  • Minimum 175g carbohydrate, 71g protein, and 28g fiber daily
  • Focus on quality carbohydrates to minimize postprandial glucose excursions
  • Avoid excessive weight gain (15-25 lbs for overweight, 10-20 lbs for obese women) 1

• Physical activity

  • 150 minutes of moderate-intensity exercise per week
  • At least 15 minutes per session, minimum 3 times weekly 1

Step 2: Blood Glucose Monitoring

• Target glucose levels:

  • Fasting: <95 mg/dL (5.3 mmol/L)
  • 1-hour postprandial: <140 mg/dL (7.8 mmol/L) or
  • 2-hour postprandial: <120 mg/dL (6.7 mmol/L) 1

• A1C target: <6% if achievable without significant hypoglycemia 1

• Monitor more frequently than usual (e.g., monthly) due to altered red blood cell kinetics 1

Step 3: Pharmacologic Therapy

• Initiate insulin therapy when lifestyle modifications fail to achieve glycemic targets 1, 2

  • No specific insulin regimen has demonstrated superiority in GDM 1
  • Insulin requirements often increase throughout second trimester and level off in third trimester 1

• Alternative medications (second-line options):

  • Glyburide: Minimal placental transfer (4%)
  • Metformin: Crosses placenta; may require supplemental insulin in 20-30% of women 2
  • Both have safety concerns and long-term offspring effects remain under investigation 2

Fetal Surveillance

• Ultrasound measurement of fetal abdominal circumference in early third trimester
• More intensive monitoring for women requiring medication
• Consider fetal testing starting at 32 weeks for women on medication 4
• Evaluate for macrosomia (estimated fetal weight >4,000g) 4

Delivery Planning

• For GDM controlled with lifestyle: deliver at 39-40 weeks
• For GDM requiring medication: deliver at 39-39+6 weeks 4
• Consider cesarean delivery if estimated fetal weight >4,500g 4

Postpartum Management

• Screen for persistent diabetes at 6-12 weeks postpartum using non-pregnancy criteria 1, 3
• Continue lifestyle modifications to reduce future diabetes risk 1
• Support breastfeeding, which may reduce obesity risk in offspring 1
• Long-term follow-up every 1-3 years to screen for diabetes development 3

Common Pitfalls to Avoid

1. Inadequate glucose monitoring: Daily self-monitoring is superior to intermittent office monitoring 1
2. Excessive caloric restriction: Can lead to ketonemia and adverse fetal outcomes 1
3. Overlooking postpartum screening: Essential for identifying women at high risk for future diabetes 1, 3
4. Neglecting long-term follow-up: Women with GDM have significantly increased lifetime risk of type 2 diabetes 1
5. Failing to recognize placental transfer of oral agents: Consider long-term effects on offspring when selecting medications 2

By following this structured approach to GDM management, providers can significantly reduce maternal and fetal complications while setting the foundation for long-term health of both mother and child.