Management of Gestational Diabetes Mellitus
Start with lifestyle modifications including medical nutrition therapy and physical activity, which successfully controls blood glucose in 70-85% of women with GDM; add insulin as the first-line pharmacological agent if glycemic targets are not met within 1-2 weeks. 1
Glycemic Targets for All Women with GDM
Monitor blood glucose with the following targets 1, 2:
- Fasting glucose <95 mg/dL (5.3 mmol/L)
- One-hour postprandial <140 mg/dL (7.8 mmol/L) OR
- Two-hour postprandial <120 mg/dL (6.7 mmol/L)
Self-monitoring of blood glucose (fasting and postprandial) is essential to assess whether lifestyle modifications alone are sufficient or pharmacological therapy is needed 1, 3.
First-Line Treatment: Lifestyle Modifications
Medical Nutrition Therapy (MNT)
Work with a registered dietitian familiar with GDM management to create an individualized meal plan that meets these specific requirements 1, 2, 3:
- Minimum 175g carbohydrate daily (amount and type of carbohydrate directly impacts postprandial glucose excursions) 1, 2
- Minimum 71g protein daily 1, 2
- 28g fiber daily 1, 2
- Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 2, 3
The carbohydrate distribution throughout the day is critical—focus on spreading carbohydrate intake across meals and snacks to prevent postprandial hyperglycemia 4. A low glycemic index diet helps avoid postprandial glucose spikes 5.
Physical Activity
Aim for at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 3. Physical activity improves glucose and insulin levels and contributes to better glycemic control 4, 6. Even unstructured physical activity incorporated into daily living can be beneficial 6.
When to Initiate Pharmacological Therapy
Add medications if lifestyle modifications fail to achieve glycemic targets within 1-2 weeks of diagnosis 1. Women with greater initial degrees of hyperglycemia (fasting ≥95 mg/dL at diagnosis) may require earlier—even immediate—initiation of pharmacologic therapy 1, 3.
Insulin: First-Line Pharmacological Agent
Insulin is the preferred and recommended first-line medication for GDM in the United States because it does not cross the placenta to a measurable extent 1, 2, 3. This is a critical safety advantage over oral agents 2.
Oral Agents: Second-Line Only
Metformin and glyburide should NOT be used as first-line agents 2, 3. Both cross the placenta to the fetus 1, 2:
- Metformin crosses the placenta to a greater extent than glyburide 1
- Glyburide has been associated with increased neonatal hypoglycemia and macrosomia compared to insulin 2
- Both agents fail to provide adequate glycemic control in 23-28% of women with GDM, requiring additional insulin 3, 5
These oral agents may be considered only when insulin cannot be prescribed or is refused by the patient 5.
Monitoring During Treatment
Glucose Monitoring
Perform fasting and postprandial self-monitoring of blood glucose daily to assess treatment effectiveness 1, 3. Postprandial monitoring is associated with better glycemic control and lower risk of preeclampsia 1.
A1C Monitoring
A1C can be used as a secondary measure but should not replace self-monitoring of blood glucose 1. Target A1C <6% (42 mmol/mol) is optimal if achievable without hypoglycemia, but may be relaxed to <7% (53 mmol/mol) if necessary 1. Monitor A1C monthly during pregnancy due to altered red blood cell kinetics 1.
Blood Pressure Monitoring
Monitor blood pressure and urinary protein at each prenatal visit, as women with GDM have increased risk of hypertensive disorders during pregnancy 2.
Common Pitfalls to Avoid
Premature initiation of medications: Remember that 70-85% of women can achieve glycemic control with lifestyle modifications alone 1, 2. Give lifestyle changes adequate time (1-2 weeks) unless initial hyperglycemia is severe 1.
Using oral agents as first-line therapy: Despite their convenience, metformin and glyburide cross the placenta and have higher failure rates than insulin 2, 3.
Inadequate carbohydrate distribution: Simply reducing total carbohydrates is insufficient—the timing and distribution of carbohydrate intake throughout the day is critical for preventing postprandial hyperglycemia 1, 4.
Delayed pharmacological therapy: Women with fasting glucose ≥95 mg/dL at diagnosis or those failing to meet targets after 1-2 weeks of lifestyle modification need prompt medication initiation 1, 3.
Telehealth Option
Telehealth visits for GDM management improve outcomes compared with standard in-person care, reducing cesarean delivery rates, neonatal hypoglycemia, and other complications 2, 3.