What is the recommended management for a pregnant patient with gestational diabetes, including medical nutrition therapy, glucose monitoring, pharmacologic treatment, fetal surveillance, timing of delivery, and postpartum follow‑up?

Management of Gestational Diabetes Mellitus

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

Initial Management: Medical Nutrition Therapy

Refer to a registered dietitian within the first week of diagnosis to develop an individualized nutrition plan that provides:

• Minimum 175 g carbohydrate daily (approximately 35% of a 2,000-calorie diet) 1, 2
• Minimum 71 g protein daily 1, 2
• Minimum 28 g fiber daily 1, 2
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats entirely 2

Distribute carbohydrates across 3 small-to-moderate meals and 2-4 snacks throughout the day, with an evening snack to prevent accelerated overnight ketosis. 2 Do not restrict carbohydrates below 175 g/day, as this may compromise fetal growth and increase maternal ketosis. 2

70-85% of women with GDM achieve adequate glycemic control with lifestyle modifications alone, eliminating the need for medication in the majority of cases. 1, 2

Glucose Monitoring Strategy

Perform daily self-monitoring of blood glucose with fasting and postprandial measurements:

• Check fasting glucose upon waking 2
• Check either 1-hour OR 2-hour postprandial glucose after each main meal (breakfast, lunch, dinner) 1, 2
• Choose consistently between 1-hour or 2-hour postprandial measurements 2

Glycemic Targets

• Fasting: <95 mg/dL (5.3 mmol/L) 1, 2
• 1-hour postprandial: <140 mg/dL (7.8 mmol/L) 1, 2
• 2-hour postprandial: <120 mg/dL (6.7 mmol/L) 1, 2

A1C has limited utility in GDM management because it may not adequately capture postprandial hyperglycemia (which drives macrosomia) and is affected by increased red blood cell turnover during pregnancy. 1 If measured, target A1C <6% (42 mmol/mol) if achievable without significant hypoglycemia, but may be relaxed to <7% (53 mmol/mol) if necessary. 1

Pharmacologic Treatment Algorithm

When to Initiate Insulin

Start insulin within 1-2 weeks if glycemic targets are not met with medical nutrition therapy alone. 1, 2 Specifically, initiate insulin when:

• Fasting glucose ≥95 mg/dL 2, 3
• 1-hour postprandial ≥140 mg/dL 2, 3
• 2-hour postprandial ≥120 mg/dL 2
• Fetal abdominal circumference ≥75th percentile on ultrasound (excessive growth) 2

Insulin Regimen

Insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent. 1, 2

Initial dosing:

• Total daily dose: 0.7-1.0 units/kg of maternal pre-pregnancy weight 2
• Distribute as approximately 40% basal insulin and 60% prandial insulin 2, 3
• Insulin requirements increase linearly by approximately 5% each week from diagnosis through week 36, often doubling by late pregnancy, requiring frequent titration 2

Rapid-acting insulin analogs (lispro, aspart) are safe for prandial coverage. 4 Limited data exist for long-acting insulin analogs, though they are increasingly used. 4

Oral Agents: Not Recommended as First-Line

Metformin and glyburide are NOT recommended as first-line therapy due to inferior outcomes and safety concerns compared to insulin. 2

Metformin concerns:

• Crosses the placenta, producing umbilical-cord concentrations equal to or higher than maternal levels 2
• Children exposed in utero had higher BMI, waist-to-height ratio, and waist circumference at age 9 years compared to insulin-exposed children 2, 3
• 25-28% of women fail to achieve glycemic targets on metformin alone, requiring additional therapy 2
• Should be avoided in women with hypertension, preeclampsia, or conditions predisposing to intrauterine growth restriction due to risk of fetal growth restriction or metabolic acidosis 2

Glyburide concerns:

• Crosses the placenta with fetal cord concentrations reaching 50-70% of maternal levels 2
• Associated with higher rates of neonatal hypoglycemia, macrosomia, and increased fetal abdominal circumference compared to insulin or metformin 2
• Failed to meet non-inferiority criteria versus insulin for composite neonatal outcomes 2
• 23% failure rate in achieving glycemic targets 2
• No long-term safety data exist for offspring 2

When oral agents may be considered:

Oral agents can be used only when insulin is impractical or unsafe due to cost, language barriers, limited health literacy, or cultural factors, or when a well-informed patient declines insulin after comprehensive counseling. 2 If an oral agent is chosen, metformin is preferred over glyburide due to lower incidences of neonatal hypoglycemia and macrosomia. 2 Patients must be counseled that all oral agents cross the placenta and long-term offspring safety data are lacking. 2

Fetal Surveillance

Begin serial ultrasound measurement of fetal abdominal circumference in the second trimester (or early third trimester) and repeat every 2-4 weeks to guide management intensity. 2, 5, 3

• When fetal abdominal circumference is <75th percentile (normal growth): Continue current management with ongoing glucose monitoring 2
• When fetal abdominal circumference is ≥75th percentile (excessive growth): Lower glycemic targets or intensify pharmacologic therapy 2, 5

Instruct women to monitor fetal movements during the last 8-10 weeks of pregnancy and report any perceived reduction immediately. 2 Women with fasting glucose >105 mg/dL or progressing beyond term require heightened surveillance for fetal demise. 2

Maternal Surveillance

Measure blood pressure and urinary protein at every prenatal visit to detect preeclampsia, which occurs 1.6-fold more frequently in women with GDM. 2, 5

Urine ketone testing may help detect inadequate caloric or carbohydrate intake in women on calorie-restricted diets, though the impact on fetal outcomes has not been evaluated. 2 Finger-stick blood ketone measurement correlates more closely with laboratory β-hydroxybutyrate levels than urine ketones. 2

Timing of Delivery

For women with diet-controlled GDM meeting glycemic targets: Delivery at 39-40 weeks of gestation is appropriate. 2

For women requiring insulin or with poor glycemic control: Delivery at 39 weeks (39⁰-39⁶ weeks) is recommended. 2, 5 Do not deliver before 38 weeks in the absence of objective evidence of maternal or fetal compromise. 5

Intrapartum Management

Monitor maternal blood glucose every 1-2 hours during labor with a target range of 80-110 mg/dL to prevent fetal hypoxia and neonatal hypoglycemia. 2, 5

• If glucose exceeds 180 mg/dL (10 mmol/L), administer an insulin bolus 2
• If glucose exceeds 297 mg/dL (16.5 mmol/L), delay non-urgent procedures and give corrective insulin 2

Switch to intravenous insulin infusion during labor or cesarean section for women requiring insulin. 3 Stop all insulin immediately after delivery and monitor blood glucose before and 2 hours after meals for 48 hours. 3

Postpartum Follow-Up

Perform a 75-g oral glucose tolerance test at 4-12 weeks postpartum using non-pregnancy diagnostic criteria to identify persistent diabetes or prediabetes. 1, 2, 5 Do NOT use A1C at this visit because the concentration may still be influenced by pregnancy changes and/or peripartum blood loss. 2

Women with a history of GDM have a 50-70% risk of developing type 2 diabetes over 15-25 years. 2 Perform lifelong screening for diabetes at least every 3 years using standard non-pregnant criteria (annual A1C, annual fasting plasma glucose, or triennial 75-g OGTT). 2

Strongly encourage breastfeeding, as it reduces future type 2 diabetes risk by 32% in women with prior GDM and provides immediate nutritional and immunologic benefits. 5 Children born to mothers with GDM have increased risk of childhood obesity and type 2 diabetes, necessitating monitoring of child development and family-wide lifestyle recommendations. 5

Critical Pitfalls to Avoid

• Do not delay insulin initiation when glycemic targets are consistently missed despite optimal medical nutrition therapy adherence 2, 3
• Do not restrict calories excessively to avoid insulin, as this causes ketosis harmful to the fetus 2, 3
• Do not rely on A1C for GDM monitoring, as altered red blood cell turnover during pregnancy makes it unreliable 2, 3
• Do not start oral agents before attempting insulin, as safety concerns of placental transfer outweigh convenience 2
• If glycemic targets are not met within 1-2 weeks of oral therapy, transition promptly to insulin or add insulin to the regimen 2
• Discontinue metformin immediately and switch to insulin if the patient develops hypertension, preeclampsia, or any sign of placental insufficiency 2