What are the management options for Gestational Diabetes Mellitus (GDM) in pregnancy?

Management of Gestational Diabetes Mellitus in Pregnancy

Start all women with GDM on lifestyle modifications (medical nutrition therapy and physical activity), and add insulin as the first-line pharmacologic agent if glycemic targets are not met—oral agents like metformin and glyburide cross the placenta and should not be used as first-line therapy. 1, 2

Glycemic Targets for GDM

Monitor blood glucose with the following specific targets 1, 2, 3:

• 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 in both fasting and postprandial states is essential, with postprandial monitoring associated with better glycemic control and lower preeclampsia risk. 3

First-Line Treatment: Lifestyle Modifications

Medical Nutrition Therapy

Work with a registered dietitian familiar with GDM management to create an individualized nutrition plan with these specific requirements 1, 2, 3:

• Minimum 175g carbohydrate daily
• Minimum 71g protein daily
• 28g fiber daily
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 2, 3

The amount and type of carbohydrate directly impact postprandial glucose excursions, so nutritional counseling should focus specifically on carbohydrate type, amount, and distribution throughout the day. 1, 4

Physical Activity

Prescribe at least 150 minutes of moderate-intensity aerobic activity per week, distributed throughout the week. 3 Exercise interventions have demonstrated improvements in glycemic outcomes and reductions in the need to initiate insulin. 3

Expected Response to Lifestyle Modifications

Approximately 70-85% of women diagnosed with GDM can achieve glycemic control with lifestyle modifications alone. 1, 2, 3 However, women with higher initial degrees of hyperglycemia or fasting glucose ≥95 mg/dL may require earlier initiation of pharmacologic therapy. 1

Second-Line Treatment: Pharmacologic Therapy

Insulin: The Preferred Agent

Insulin is the first-line pharmacologic agent because it does not cross the placenta to a measurable extent. 1, 2, 3 Treatment with insulin has been demonstrated to improve perinatal outcomes in large randomized studies. 1

Oral Agents: Second-Line Options with Caveats

Both metformin and glyburide cross the placenta and should not be used as first-line agents. 1, 2, 3 If oral agents are considered:

Metformin:

• Crosses the placenta with umbilical cord blood levels higher than maternal levels 1
• Associated with lower risk of neonatal hypoglycemia and less maternal weight gain compared to insulin 1
• May slightly increase risk of prematurity 1
• Nearly half of patients initially treated with metformin require insulin to achieve acceptable glucose control 1
• Likely crosses the placenta to a greater extent than glyburide 1

Glyburide:

• Umbilical cord plasma concentrations approximately 70% of maternal levels 1
• Associated with higher rates of neonatal hypoglycemia and macrosomia compared to insulin or metformin 1, 2
• Has minimal placental transfer compared to metformin but still crosses 2

Critical caveat: Patients treated with oral agents must be informed that these medications cross the placenta, and although no adverse effects on the fetus have been demonstrated in short-term studies, long-term safety data are not available for any oral agent. 1

Monitoring During Pregnancy

• Monitor blood pressure and urinary protein at each prenatal visit, as women with GDM have increased risk of hypertensive disorders during pregnancy 2
• For patients requiring medications or with poor glucose control, initiate fetal surveillance starting at 32 weeks of gestation 5
• Assess for fetal macrosomia (estimated fetal weight >4,000g) and discuss risks/benefits of prelabor cesarean delivery if estimated fetal weight >4,500g 5

Delivery Timing

• For women controlling glucose with lifestyle modifications alone: Deliver at 39/0 to 40/6 weeks of gestation 5
• For women requiring medications: Deliver at 39/0 to 39/6 weeks of gestation 5

Common Pitfalls to Avoid

Do not prematurely initiate pharmacologic therapy. The majority (70-85%) of women can manage GDM with lifestyle modification alone, and unnecessary medication use exposes the fetus to agents that cross the placenta. 1, 2

Do not assume oral antihyperglycemic agents are equivalent to insulin in safety and efficacy. Both metformin and glyburide cross the placenta, lack long-term safety data, and have been associated with specific adverse outcomes. 1, 2

Do not rely solely on HbA1c for glycemic monitoring in pregnancy. A1C levels fall during normal pregnancy due to physiological increases in red blood cell turnover and may not fully capture postprandial hyperglycemia that drives macrosomia—self-monitoring of blood glucose is essential. 1