How is gestational diabetes mellitus (GDM) managed?

Management of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) should be managed initially with lifestyle modifications, with insulin added if glycemic targets are not achieved, as insulin is the preferred medication for treating hyperglycemia in GDM due to its safety profile and inability to cross the placenta. 1

Diagnostic Targets and Monitoring

Blood glucose monitoring should aim for the following targets:

• Fasting glucose <95 mg/dL (<5.3 mmol/L) and either
• One-hour postprandial glucose <140 mg/dL (<7.8 mmol/L) or
• Two-hour postprandial glucose <120 mg/dL (<6.7 mmol/L) 1

Management Algorithm

Step 1: Lifestyle Modifications (First-Line Treatment)

Approximately 70-85% of women diagnosed with GDM can achieve glycemic control with lifestyle modifications alone 1.

Medical Nutrition Therapy

• Individualized nutrition plan developed with a registered dietitian 1
• Dietary recommendations:
  • Minimum 175 g carbohydrate (35% of a 2,000-calorie diet)
  • Minimum 71 g protein
  • 28 g fiber 1
  • Emphasize monounsaturated and polyunsaturated fats
  • Limit saturated fats and avoid trans fats 1
  • Focus on type, amount, and distribution of carbohydrates to limit postprandial glucose excursions 2

Physical Activity

• Regular exercise improves glucose outcomes and reduces insulin requirements 1
• Effective exercise includes:
  • 20-50 minutes per day
  • 2-7 days per week
  • Moderate intensity
  • Can be aerobic, resistance, or both 1

Step 2: Pharmacological Therapy (When Lifestyle Modifications Fail)

Insulin Therapy (First-Line Medication)

• Add insulin when lifestyle modifications fail to achieve glycemic targets 1
• Advantages of insulin:
  • Does not cross the placenta to a measurable extent 1, 3
  • Can be precisely titrated to achieve glycemic targets 3
  • Demonstrated improvement in perinatal outcomes in randomized studies 1

Alternative Medications (Not First-Line)

• Metformin and glyburide should not be used as first-line agents 1
• Both medications cross the placenta and lack long-term safety data 1

Metformin Concerns:

• Crosses the placenta readily 1
• Umbilical cord blood levels can be higher than maternal levels 1
• Associated with higher BMI and increased obesity in offspring at follow-up 1, 3
• 25-46% of women may require additional insulin to maintain glycemic control 1, 4

Sulfonylureas (Glyburide) Concerns:

• Concentrations in umbilical cord plasma are approximately 50-70% of maternal levels 1
• Associated with increased neonatal hypoglycemia and macrosomia compared to insulin 1
• Failed to be found non-inferior to insulin based on composite neonatal outcomes 1, 3

Post-Delivery Management

• Glucose testing shortly after delivery to stratify short-term diabetes risk 5
• Annual glucose and HbA1c testing to detect deteriorating glycemic control 5
• Encourage breastfeeding to potentially reduce obesity in children 5
• Counsel women about increased risks of:
  • Type 2 diabetes mellitus
  • Hypertensive disorders
  • Cardiovascular diseases
  • Metabolic syndrome 4, 6

Common Pitfalls and Caveats

1. Delayed insulin initiation: Poor glycemic control increases risks of adverse maternal and fetal outcomes. Don't hesitate to start insulin when lifestyle modifications fail 3.

2. Relying on oral agents: Despite some evidence supporting metformin and glyburide efficacy, their use as first-line agents is not recommended due to placental crossing and lack of long-term safety data 1.

3. Inadequate monitoring: Regular blood glucose monitoring is essential regardless of treatment approach 3.

4. Insufficient dietary guidance: Nutritional counseling should specifically address carbohydrate type, amount, and distribution rather than just general healthy eating 2.

5. Overlooking postpartum follow-up: Women with GDM have increased risk of developing type 2 diabetes and should receive appropriate screening and preventive interventions after delivery 5, 6.