Primary Treatment for Gestational Diabetes Mellitus
Medical nutrition therapy (MNT) is the cornerstone and first-line treatment for all women diagnosed with GDM, and should be initiated immediately upon diagnosis with referral to a registered dietitian within the first week. 1, 2
Initial Management Algorithm
Step 1: Immediate Lifestyle Interventions
Nutritional therapy forms the foundation of GDM management and should be prescribed by a registered dietitian experienced in GDM care. 3, 1 The specific dietary requirements include:
- Minimum 175 g carbohydrate daily (never reduce below this threshold as it may compromise fetal growth) 1, 2
- 71 g protein daily 1, 2
- 28 g fiber daily 1, 2
- Emphasis on monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1, 2
- Total caloric intake of approximately 2,000-2,200 kcal/day for overweight women, calculated as 30-32 kcal/kg of pre-pregnancy body weight plus an additional 340 kcal/day in the second trimester 1
Physical activity should be prescribed concurrently, with at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week. 1, 2
Step 2: Blood Glucose Monitoring
Self-monitoring of blood glucose must begin immediately with the following targets: 1, 2
- Fasting glucose <95 mg/dL
- 1-hour postprandial <140 mg/dL
- 2-hour postprandial <120 mg/dL
Check fasting glucose daily upon waking and postprandial glucose after each main meal (breakfast, lunch, dinner). 1
Step 3: Decision Point for Pharmacologic Therapy
If glycemic targets are not achieved within 1-2 weeks of lifestyle modifications alone, insulin therapy must be initiated as the first-line pharmacologic agent. 1, 2 This is a critical decision point—approximately 70-85% of women achieve glycemic control with lifestyle modifications alone, but those who don't require prompt escalation. 2
Pharmacologic Management When Needed
Insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent. 1, 2 There is no evidence demonstrating superiority of a particular insulin or insulin analog regimen; administration should be individualized to achieve glycemic goals. 3
Important Caveat on Oral Agents
The Endocrine Society recommends avoiding metformin and glyburide as first-line therapy due to their inferior outcomes and safety profiles compared to insulin. 1 Both agents cross the placenta and fail to provide adequate glycemic control in 23-28% of women with GDM. 2
However, the evidence shows some nuance: glyburide has minimal placental transfer (4% ex vivo) and one randomized controlled trial supports its use as an adjunct when additional therapy is needed, though it may be less successful in obese patients or those with marked hyperglycemia. 3 Despite this, current guidelines prioritize insulin over oral agents for initial pharmacologic management. 1, 2
Common Pitfalls to Avoid
Do not delay pharmacologic therapy if lifestyle modifications fail to achieve targets within 1-2 weeks—this increases risks of fetal macrosomia and other complications. 1, 2
Do not restrict carbohydrates below 175 g/day, as this may compromise fetal growth when total energy intake is inadequate. 1
Avoid starvation ketosis—monitor for ketonemia and ensure adequate energy intake that provides appropriate weight gain. 3
Do not use metformin or glyburide as first-line agents when insulin is available and appropriate, given their inferior safety and efficacy profiles. 1, 2
Monitoring for Treatment Escalation
Women who fail to maintain glycemic goals or who show signs of excessive fetal growth should receive intensified metabolic therapy beyond standard nutritional management. 3 Those with greater initial degrees of hyperglycemia may require earlier initiation of pharmacological therapy. 2