What is the recommended management for a pregnant woman diagnosed with Gestational Diabetes Mellitus (GDM)?

Management of Gestational Diabetes Mellitus

Begin immediately with medical nutrition therapy and self-monitoring of blood glucose, targeting fasting glucose <95 mg/dL, 1-hour postprandial <140 mg/dL, or 2-hour postprandial <120 mg/dL; if these targets are not achieved within 1-2 weeks with lifestyle modifications alone, initiate insulin therapy as the first-line pharmacologic agent. 1

Initial Diagnostic Confirmation and Immediate Actions

Once GDM is diagnosed (fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, or 2-hour ≥153 mg/dL on 75-g OGTT), start treatment immediately without delay. 1 The cornerstone of management is lifestyle modification, which successfully controls glucose in 70-85% of women with GDM. 2

Medical Nutrition Therapy (First-Line Treatment)

Refer to a registered dietitian familiar with GDM management within the first week of diagnosis. 1 The dietary prescription must include mandatory minimums that are non-negotiable:

• Minimum 175 grams of carbohydrate daily - never reduce below this threshold as it risks fetal growth compromise and maternal ketosis 1, 3
• Minimum 71 grams of protein daily 1, 3
• Minimum 28 grams of fiber daily 1, 3

Distribute carbohydrates across 3 small-to-moderate meals and 2-4 snacks throughout the day, with an evening snack usually necessary to prevent accelerated overnight ketosis. 3 Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats. 1, 3

Critical pitfall to avoid: Never prescribe hypocaloric diets <1,200 kcal/day, which cause ketonemia and compromise fetal development. 3

Physical Activity Prescription

Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week. 1 Regular aerobic exercise lowers fasting and postprandial glucose and should be used as an adjunct to nutrition therapy. 3 This can be as simple as encouraging 30 minutes of walking on most days of the week. 4, 5

Blood Glucose Monitoring Protocol

Check fasting glucose daily upon waking and postprandial glucose after each main meal (breakfast, lunch, dinner). 1 Choose either 1-hour postprandial OR 2-hour postprandial measurements consistently - do not alternate between the two. 1

Glycemic targets are:

• Fasting <95 mg/dL 2, 1
• 1-hour postprandial <140 mg/dL 2, 1
• 2-hour postprandial <120 mg/dL 2, 1

Postprandial monitoring is superior to preprandial monitoring alone and is associated with better glycemic control and lower risk of preeclampsia. 1

Pharmacologic Therapy (When Lifestyle Fails)

If glycemic targets are not achieved within 1-2 weeks of medical nutrition therapy alone, initiate insulin as first-line pharmacologic therapy. 1, 3 Insulin is the preferred and recommended agent because it does not cross the placenta to a measurable extent. 2, 1

Why Insulin Over 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 While individual trials have shown efficacy for metformin and glyburide, both agents cross the placenta to the fetus. 2 Specifically:

• Glyburide: Umbilical cord concentrations reach approximately 70% of maternal levels and is associated with higher rates of neonatal hypoglycemia and macrosomia compared to insulin. 2
• Metformin: Crosses the placenta to an even greater extent than glyburide, and nearly half of patients initially treated with metformin require insulin to achieve acceptable glucose control. 2 Long-term safety data are not available for any oral agent. 2

Insulin Dosing Principles

In general, a small proportion of the total daily dose should be given as basal insulin and a greater proportion as prandial insulin. 2 All insulins are pregnancy category B except for glargine and glulisine, which are labeled C. 2 Due to the complexity of insulin management in pregnancy, referral to a specialized center is recommended if this resource is available. 2

Fetal and Maternal Surveillance

Begin ultrasound monitoring of fetal abdominal circumference in the second and early third trimesters, repeating every 2-4 weeks. 1 When fetal abdominal circumference is excessive (≥75th percentile), consider lower glycemic targets or intensification of pharmacologic therapy. 1

Measure blood pressure and urinary protein at each prenatal visit to detect preeclampsia, as the risk of hypertensive disorders is increased in women with GDM. 1 Teach mothers to monitor fetal movements during the last 8-10 weeks of pregnancy and report immediately any reduction. 1

HbA1c Monitoring (Secondary Measure Only)

HbA1c has limited utility in GDM management but should be measured monthly if used, with a target HbA1c <6% if achievable without significant hypoglycemia. 1 HbA1c should NOT replace blood glucose monitoring because macrosomia results primarily from postprandial hyperglycemia, which HbA1c may not adequately detect. 1 Due to increased red blood cell turnover during pregnancy, A1C levels fall and may not fully capture physiologically relevant glycemic parameters. 2

Delivery Timing

Delivery timing depends on glycemic control: delivery at 39-40 weeks of gestation is appropriate for women with diet-controlled GDM meeting glycemic targets, and delivery at 39 weeks of gestation is recommended for women requiring insulin or with poor glycemic control. 1 Assess for fetal macrosomia (estimated fetal weight >4,000 g) and discuss the risks and benefits of prelabor cesarean delivery if the estimated fetal weight is >4,500 g. 6

Postpartum Management

All women with GDM must be tested for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75-g oral glucose tolerance test (OGTT) with non-pregnancy diagnostic criteria. 1 Do NOT use HbA1c at this visit because the concentration may still be influenced by changes during pregnancy and/or peripartum blood loss. 1

Women with a history of GDM have a 50-70% risk of developing type 2 diabetes over 15-25 years, and require lifelong screening for diabetes at least every 3 years. 1 All women should be supported in attempts to breastfeed their babies, given immediate nutritional and immunological benefits; there may also be a longer-term metabolic benefit to both mother and offspring. 2