What is the management of Gestational Diabetes Mellitus (GDM)?

Management of Gestational Diabetes Mellitus

Lifestyle modification with medical nutrition therapy and physical activity is the first-line treatment for GDM, and if glycemic targets are not achieved, insulin should be added as the preferred pharmacologic agent. 1

Initial Management: Lifestyle Modifications

Medical Nutrition Therapy

• All women with GDM should receive individualized medical nutrition therapy from a registered dietitian nutritionist (RDN) familiar with GDM management. 1
• The diet must provide adequate calories for fetal and maternal health while achieving glycemic control and appropriate gestational weight gain according to 2009 National Academy of Medicine recommendations. 1
• Minimum daily requirements include 175g carbohydrates, 71g protein, and 28g fiber. 1, 2
• Distribute carbohydrates across three small-to-moderate meals and two-to-four snacks throughout the day to limit postprandial glucose excursions. 2
• Focus on carbohydrate type, amount, and distribution—simple carbohydrates cause higher postmeal excursions, so emphasize complex carbohydrates, fiber-rich foods, fruits, vegetables, nuts, seeds, fish, and lean protein. 1, 3

Physical Activity

• Recommend at least 150 minutes of moderate-intensity aerobic activity per week during pregnancy, preferably spread throughout the week. 1
• Exercise improves glucose outcomes and reduces the need for insulin or insulin dose requirements, though optimal exercise type (aerobic, resistance, or both) and duration (20-50 minutes/day, 2-7 days/week) remain heterogeneous. 1

Expected Outcomes with Lifestyle Alone

• 70-85% of women diagnosed with GDM under Carpenter-Coustan criteria can achieve glycemic control with lifestyle modifications alone; this proportion is anticipated to be even higher with lower International Association of Diabetes and Pregnancy Study Groups diagnostic thresholds. 1

Glycemic Targets

Monitor blood glucose aiming for these targets recommended by the Fifth International Workshop-Conference on Gestational Diabetes Mellitus: 1

• Fasting glucose <95 mg/dL (5.3 mmol/L)
• One-hour postprandial glucose <140 mg/dL (7.8 mmol/L) OR
• Two-hour postprandial glucose <120 mg/dL (6.7 mmol/L)

Pharmacologic Therapy

When to Initiate Medication

• Add insulin if glycemic targets are not achieved with lifestyle modifications alone. 1
• Women with greater initial degrees of hyperglycemia may require earlier initiation of pharmacologic therapy. 1
• Obese women with GDM in the third trimester frequently require insulin due to increased insulin resistance. 2

First-Line Pharmacologic Agent: Insulin

Insulin is the preferred medication for treating hyperglycemia in GDM because it does not cross the placenta to a measurable extent. 1, 2

Insulin Dosing and Regimen

• Calculate initial total daily insulin dose as 0.7-1.0 units/kg of current weight (approximately 0.8 units/kg recommended for obese women in third trimester). 2
• Distribute as 40% basal insulin (NPH or long-acting analogs) and 60% prandial insulin (regular or rapid-acting analogs). 2
• Administer basal insulin in two doses: 2/3 in the morning and 1/3 at night. 2
• Distribute prandial insulin before main meals based on carbohydrate content. 2

Insulin Monitoring and Adjustments

• Monitor fasting and postprandial blood glucose daily. 2
• Adjust insulin doses weekly or biweekly, increasing by 10-20% if targets are not met. 2
• In the third trimester, insulin resistance increases exponentially, requiring more frequent adjustments. 2
• A rapid and significant reduction in insulin requirements may indicate placental insufficiency, though data are conflicting. 1

Important Insulin Safety Considerations

• Provide guidance on hypoglycemia recognition and treatment. 2
• Monitor ketonuria to prevent fasting ketosis. 2
• Include a bedtime snack to prevent nocturnal hypoglycemia and accelerated ketosis. 2

Oral Agents: Not Recommended as First-Line

Metformin and glyburide should not be used as first-line agents because both cross the placenta to the fetus. 1

Metformin

• Metformin crosses the placenta, with umbilical cord blood levels as high or higher than maternal levels. 1, 4
• In the MiG TOFU study, 9-year-old offspring exposed to metformin were heavier with higher waist-to-height ratio and waist circumference than those exposed to insulin (Auckland cohort). 1
• Metformin failed to provide adequate glycemic control in 25-28% of women with GDM in randomized controlled trials. 1
• The FDA label states that limited data with metformin in pregnant women are not sufficient to determine drug-associated risk for major birth defects or miscarriage. 4

Glyburide

• Glyburide crosses the placenta with umbilical cord plasma concentrations approximately 50-70% of maternal levels. 1
• Glyburide was associated with higher rates of neonatal hypoglycemia and macrosomia than insulin or metformin. 1
• Glyburide failed to provide adequate glycemic control in 23% of women with GDM. 1
• Long-term safety data for offspring exposed to glyburide are not available. 1

Other Oral and Injectable Agents

• Other oral and noninsulin injectable glucose-lowering medications lack long-term safety data. 1

Telehealth and Team-Based Care

• Telehealth visits for pregnant people with GDM improve outcomes compared with standard in-person care, demonstrating reductions in cesarean delivery, neonatal hypoglycemia, premature rupture of membranes, macrosomia, pregnancy-induced hypertension or preeclampsia, preterm birth, neonatal asphyxia, and polyhydramnios. 1
• Team-based care through specialized centers or interprofessional team members is recommended. 1

Common Pitfalls to Avoid

• Do not use metformin for polycystic ovary syndrome beyond the first trimester—it should be discontinued by the end of the first trimester. 1
• Do not rely solely on A1C for monitoring as it represents an average and may not capture physiologically relevant glycemic parameters in pregnancy due to increased red blood cell turnover. 1
• Do not delay insulin initiation in women with poor glycemic control on lifestyle modifications, as treatment improves perinatal outcomes. 1