What is the management of Gestational Diabetes Mellitus (GDM) across the 1st, 2nd, and 3rd trimesters?

Management of Gestational Diabetes Mellitus Across Trimesters

Lifestyle modifications are the cornerstone of GDM management across all trimesters, with insulin as the preferred pharmacological therapy when glycemic targets are not achieved. 1

First Trimester

Screening and Initial Management

• Screen high-risk women in early pregnancy (first trimester)
• For women with polycystic ovary syndrome on metformin, discontinue by the end of the first trimester 1
• Begin lifestyle interventions early, as they can reduce GDM risk when started in first or early second trimester 1

Nutritional Management

• Implement individualized medical nutrition therapy (MNT) with a registered dietitian
• Ensure adequate caloric intake based on National Academy of Medicine recommendations
• Provide minimum 175g carbohydrate, 71g protein, and 28g fiber daily 1
• Focus on quality carbohydrates with low glycemic index 2
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1

Second Trimester

Screening and Diagnosis

• Universal screening at 24-28 weeks for women not previously diagnosed
• Begin monitoring with the following glycemic targets:
  • Fasting: <95 mg/dL (5.3 mmol/L)
  • 1-hour postprandial: <140 mg/dL (7.8 mmol/L) or
  • 2-hour postprandial: <120 mg/dL (6.7 mmol/L) 1

Management Approach

• Continue MNT and physical activity as first-line therapy
• Monitor fetal growth with ultrasound measurements of fetal abdominal circumference starting in second trimester 1
• Adjust management based on fetal growth measurements:
  • Normal growth (abdominal circumference <75th percentile): Continue standard management
  • Excessive growth: Consider lower glycemic targets or add/intensify pharmacological therapy 1

Physical Activity

• Recommend at least 150 minutes of moderate-intensity aerobic activity weekly 1
• Exercise interventions (20-50 min/day, 2-7 days/week) improve glucose outcomes and reduce insulin requirements 1
• Both aerobic and resistance exercises can be beneficial 1

Third Trimester

Intensified Management

• Continue monitoring fetal growth every 2-4 weeks via ultrasound 1
• Monitor for insulin requirement changes - requirements typically level off toward the end of the third trimester 1
• Be alert for rapid reduction in insulin requirements, which may indicate placental insufficiency 1

Pharmacological Therapy

• Add insulin if glycemic targets are not achieved with lifestyle modifications
• Insulin is the preferred medication for treating hyperglycemia in GDM 1, 3
• Insulin does not cross the placenta to a measurable extent and can be individually titrated 1
• Alternative medications (only if insulin cannot be used):
  • Metformin: Crosses the placenta; associated with lower risk of neonatal hypoglycemia but may increase risk of prematurity; long-term safety concerns include potential for higher BMI in offspring 1
  • Glyburide: Crosses the placenta (50-70% of maternal levels); associated with increased neonatal hypoglycemia and macrosomia 1

Important Considerations Across All Trimesters

Monitoring

• Regular self-monitoring of blood glucose to achieve glycemic targets
• Consider ketone monitoring in patients with severe hyperglycemia or weight loss 1
• A1C may be used as a secondary measure of glycemic control, with target of 6-6.5% (42-48 mmol/mol) 1

Treatment Success Rates

• 70-85% of women diagnosed with GDM can achieve glycemic control with lifestyle modifications alone 1
• Remaining 15-30% will require pharmacological therapy, primarily insulin 1

Delivery Planning

• Women with diet-controlled GDM can await spontaneous labor
• Women requiring insulin or with poor glycemic control may need elective delivery at term 4

Pitfalls and Caveats

• Avoid starvation ketosis - ensure adequate caloric intake 1
• Do not delay insulin initiation when indicated, as poor glycemic control increases adverse outcomes
• Remember that oral agents cross the placenta and lack long-term safety data 1
• A rapid reduction in insulin requirements in late pregnancy may signal placental insufficiency 1
• Metformin and glyburide should not be used as first-line agents due to placental crossing and safety concerns 1

By following this trimester-specific approach to GDM management with appropriate lifestyle modifications and timely addition of insulin when needed, maternal and fetal outcomes can be optimized throughout pregnancy.