What is the management plan for a pregnant individual with an abnormal glucose challenge test result indicating gestational diabetes mellitus (GDM)?

Management of Abnormal Glucose Challenge Test in Pregnancy

If a pregnant individual has an abnormal glucose challenge test (GCT), proceed immediately to confirmatory testing with a 75-g oral glucose tolerance test (OGTT) using the one-step approach or complete the two-step approach with a 100-g OGTT, and upon diagnosis of gestational diabetes mellitus (GDM), initiate medical nutrition therapy and self-monitoring of blood glucose within the first week, with insulin as first-line pharmacologic therapy if glycemic targets are not achieved within 1-2 weeks. 1

Diagnostic Confirmation

Two-Step Approach (If Using 50-g GCT)

• Complete the diagnostic process with a fasting 100-g OGTT if the 1-hour glucose after the 50-g load is ≥130-140 mg/dL (thresholds vary by institution) 2
• Diagnose GDM if at least two of the following four values are met or exceeded using Carpenter-Coustan criteria: fasting ≥95 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥155 mg/dL, 3-hour ≥140 mg/dL 2
• Note that ACOG states one elevated value can be used for diagnosis, though traditionally two values are required 2

One-Step Approach (Alternative)

• Perform a 75-g OGTT at 24-28 weeks if not already done, with diagnosis made when any single value meets or exceeds: fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, or 2-hour ≥153 mg/dL 2, 1
• Only one abnormal value is required for diagnosis with this approach 1

Immediate Management After GDM Diagnosis

Lifestyle Interventions (First-Line for All)

• Refer to a registered dietitian within the first week of diagnosis for individualized medical nutrition therapy 1
• Prescribe specific dietary targets: minimum 175 g carbohydrate daily, 71 g protein daily, 28 g fiber daily, emphasizing mono- and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1
• Recommend physical activity: at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week, if not contraindicated 2, 1

Blood Glucose Monitoring

• Initiate self-monitoring with fasting glucose checked daily upon waking and postprandial glucose after each main meal (breakfast, lunch, dinner) 1
• Target glycemic goals: fasting <95 mg/dL, 1-hour postprandial <140 mg/dL, OR 2-hour postprandial <120 mg/dL 2, 1
• These targets are based on the Fifth International Workshop-Conference on Gestational Diabetes Mellitus and are consistently recommended across guidelines 2

Pharmacologic Therapy Decision Algorithm

When to Initiate Medication

• Start insulin therapy if glycemic targets are not achieved within 1-2 weeks of lifestyle modifications alone 1
• Approximately 70-85% of patients diagnosed under Carpenter-Coustan criteria can manage GDM with lifestyle alone; this proportion is expected to be higher with the lower IADPSG diagnostic thresholds 2

First-Line Pharmacologic Agent

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

Agents to Avoid as First-Line

• Do not use metformin or glyburide as first-line therapy due to inferior outcomes and safety profiles compared to insulin 1
• Both metformin and glyburide cross the placenta, and data on long-term safety for offspring is concerning 2
• Glyburide was associated with higher rates of neonatal hypoglycemia and macrosomia than insulin in meta-analyses 2
• Metformin and glyburide failed to provide adequate glycemic control in 25-28% and 23% of women with GDM, respectively 2

Special Consideration for Metformin

• Discontinue metformin by the end of the first trimester if it was being used to treat polycystic ovary syndrome and induce ovulation 2

Fetal and Maternal Monitoring

Fetal Surveillance

• Initiate fetal surveillance starting at 32 weeks of gestation for patients with poor glucose control or who require medications 3
• Regular obstetric examinations including ultrasound are recommended to monitor for fetal macrosomia 4

Delivery Planning

• Assess for fetal macrosomia (estimated fetal weight >4,000 g) and discuss risks/benefits of prelabor cesarean delivery if estimated fetal weight is >4,500 g 3
• Recommended delivery timing: 39/0 to 40/6 weeks for those controlling glucose with lifestyle alone; 39/0 to 39/6 weeks for those requiring medications 3

Postpartum Management

Immediate Postpartum Period

• Insulin resistance decreases dramatically immediately postpartum, and insulin requirements need evaluation and adjustment as they are often roughly half the prepregnancy requirements for the initial few days 2
• Discuss and implement a contraceptive plan with all women with diabetes of reproductive potential 2

Postpartum Testing for Persistent Diabetes

• Test for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75-g OGTT with non-pregnancy diagnostic criteria 2, 1
• The OGTT is recommended over A1C because A1C may be persistently lowered by increased red blood cell turnover related to pregnancy, blood loss at delivery, or the preceding 3-month glucose profile 2
• Diagnose diabetes if both fasting plasma glucose ≥126 mg/dL AND 2-hour plasma glucose ≥200 mg/dL are abnormal in a single test 2
• If only one value meets diabetes criteria, repeat the test to confirm the abnormality persists 2

Long-Term Follow-Up

• Screen every 1-3 years thereafter if the 4-12 weeks postpartum OGTT is normal, as women with GDM have a 50-70% risk of developing type 2 diabetes over 15-25 years 2, 1
• The absolute risk increases linearly: approximately 20% at 10 years, 30% at 20 years, 40% at 30 years, 50% at 40 years, and 60% at 50 years 2

Diabetes Prevention Strategies

• Provide intensive lifestyle interventions or metformin to women with prediabetes found at postpartum testing to prevent progression to diabetes 2
• Both interventions reduce progression to diabetes by 35-40% over 10 years compared with placebo, with only 5-6 individuals needing treatment to prevent one case of diabetes over 3 years 2
• Recommend breastfeeding to reduce the risk of maternal type 2 diabetes 2
• Weight loss is recommended in the postpartum period for those with overweight/obesity 2

Common Pitfalls to Avoid

• Do not use A1C for postpartum screening at 4-12 weeks as it lacks sensitivity due to pregnancy-related changes in red blood cell turnover 2
• Do not prescribe ACE inhibitors, angiotensin receptor blockers, or statins during pregnancy as they are potentially harmful and contraindicated 2
• Do not perform OGTT after bariatric surgery due to risk of postprandial hypoglycemia 4
• Do not delay insulin initiation beyond 1-2 weeks if lifestyle modifications fail to achieve glycemic targets, as this increases risks of adverse outcomes 1