What is the treatment approach for gestational diabetes (GD) not controlled with diet, specifically using metformin?

Management of Gestational Diabetes Not Controlled with Diet: Role of Metformin

Insulin is the preferred medication for treating gestational diabetes mellitus (GDM) not controlled with diet, while metformin should not be used as a first-line agent due to placental crossing and concerns about long-term safety for offspring. 1

Treatment Algorithm for GDM

1. Initial Management: Lifestyle Modifications

   • Medical nutrition therapy with individualized meal planning
   • Physical activity
   • Weight management
   • Blood glucose monitoring with targets:
     • Fasting glucose <95 mg/dL
     • One-hour postprandial <140 mg/dL or
     • Two-hour postprandial <120 mg/dL 1

2. When Lifestyle Modifications Fail:

   • First-line pharmacologic therapy: INSULIN
   • Approximately 15-30% of women with GDM will require medication beyond lifestyle modifications 1

Evidence Against Metformin as First-Line Therapy

Despite some potential advantages, metformin has significant limitations:

• Placental transfer concerns: Metformin readily crosses the placenta, resulting in umbilical cord blood levels as high or higher than maternal levels 1, 2

• Inadequate glycemic control: Metformin fails to provide adequate glycemic control in 25-28% of women with GDM, requiring supplemental insulin 1

• Long-term offspring concerns: Follow-up studies of children exposed to metformin in utero showed:

  • Higher BMI and increased obesity at 4 years of age
  • Higher waist-to-height ratio and waist circumference at 9 years
  • Higher weight-to-height ratios at 5-10 years 1, 2

Limited Scenarios for Metformin Use

Metformin may be considered in specific situations:

• Women who cannot use insulin safely due to:
  • Cost barriers
  • Language barriers
  • Comprehension issues
  • Cultural influences 1

However, this should only occur after thorough discussion of known risks and the need for more long-term safety data in offspring 1.

Important Contraindications for Metformin in GDM

Metformin should not be used in women with:

• Hypertension
• Preeclampsia
• Risk for intrauterine growth restriction 1

Potential Benefits of Metformin (Despite Not Being First-Line)

Some studies have shown metformin may offer certain advantages compared to insulin:

• Lower risk of maternal hypoglycemia
• Less maternal weight gain 3
• Better postprandial glycemic control for some meals 3

Insulin Administration

When insulin is needed:

• Both multiple daily insulin injections and continuous subcutaneous insulin infusion are reasonable delivery strategies
• Neither has been shown to be superior during pregnancy 1

Key Pitfalls to Avoid

1. Continuing metformin for PCOS: Metformin used for polycystic ovary syndrome should be discontinued by the end of the first trimester 1, 2

2. Using oral agents without informed consent: Always discuss with patients that metformin crosses the placenta and long-term safety data is lacking 1

3. Inadequate monitoring: Regular blood glucose monitoring is essential regardless of treatment approach 1

4. Delayed insulin initiation: Do not delay starting insulin when indicated, as poor glycemic control increases risks of adverse maternal and fetal outcomes 1