Management of Gestational Diabetes Mellitus
Start all women with GDM on lifestyle modifications (medical nutrition therapy and physical activity), which successfully controls glucose in 70-85% of cases; add insulin as first-line pharmacological therapy only when glycemic targets are not met with lifestyle changes alone. 1
Glycemic Targets
Aim for these specific glucose thresholds to guide treatment decisions 1:
- Fasting glucose <95 mg/dL
- One-hour postprandial <140 mg/dL
- Two-hour postprandial <120 mg/dL
Self-monitoring of blood glucose is essential to assess whether targets are being met 1.
First-Line: Lifestyle Modifications
Medical Nutrition Therapy (MNT)
Work with a registered dietitian to create an individualized plan that meets these specific requirements 1, 2:
- Minimum 175g carbohydrate daily
- Minimum 71g protein daily
- 28g fiber daily
- Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1
The carbohydrate type, amount, and distribution throughout the day are critical since postprandial glucose excursions depend directly on carbohydrate intake 2. Focus on low glycemic index foods to avoid postprandial hyperglycemia 3.
Physical Activity
Regular physical activity has beneficial effects on glucose and insulin levels and contributes to better glycemic control 2, 4.
Monitoring Response
Continue lifestyle modifications alone if glycemic targets are consistently met 1. Telehealth visits for GDM patients improve outcomes compared with standard in-person care 1.
Second-Line: Pharmacological Therapy
When to Initiate Medication
Add pharmacological therapy when lifestyle modifications fail to achieve the glycemic targets listed above 1, 3.
Insulin: Preferred First-Line Agent
Insulin is the preferred medication because it does not cross the placenta to a measurable extent 1, 5:
- Rapid-acting analogues (aspart, lispro) achieve postprandial targets with less hypoglycemia compared to regular insulin 5
- Long-acting analogues (glargine, detemir) appear safe with similar maternal/fetal outcomes compared to NPH insulin 5
Oral Agents: Not First-Line
Metformin and glyburide should not be used as first-line agents because both cross the placenta 1, 5:
Metformin has good efficacy and short-term safety data but freely crosses the placenta and lacks long-term safety data 5. Up to 46% of women on metformin may require additional insulin to maintain glucose control 3.
Glyburide has minimal placental transfer but is associated with increased neonatal hypoglycemia and macrosomia compared to insulin 1, 5.
Additional Monitoring
Monitor blood pressure and urinary protein at each prenatal visit, as women with GDM have increased risk of hypertensive disorders during pregnancy 1.
For patients requiring medications or with poor glucose control, initiate fetal surveillance starting at 32 weeks of gestation 6.
Common Pitfalls
Avoid unnecessarily starting medications in the 70-85% of women who can achieve glycemic control with lifestyle modifications alone 1. This requires adequate time (typically 1-2 weeks) to assess response to dietary changes and physical activity before escalating to pharmacological therapy.
Do not assume oral antihyperglycemic agents are equivalent to insulin in safety and efficacy 1. The placental transfer of metformin and glyburide raises concerns about long-term offspring outcomes that are not present with insulin.