What are the recommended monitoring and management strategies for a pregnant woman with Gestational Diabetes Mellitus (GDM)?

Monitoring and Management of Gestational Diabetes Mellitus

Women with GDM should perform daily fasting and postprandial blood glucose monitoring, targeting fasting glucose <95 mg/dL, 1-hour postprandial <140 mg/dL, or 2-hour postprandial <120 mg/dL, with immediate initiation of medical nutrition therapy and insulin as first-line pharmacologic therapy if targets are not met within 1-2 weeks. 1, 2

Blood Glucose Monitoring Strategy

Self-monitoring of blood glucose is the cornerstone of GDM management and must be performed multiple times daily:

• Check fasting glucose daily upon waking 2
• Check postprandial glucose after each main meal (breakfast, lunch, dinner) 2
• Choose either 1-hour postprandial OR 2-hour postprandial measurements consistently 1
• Postprandial monitoring is superior to preprandial monitoring alone and is associated with better glycemic control and lower risk of preeclampsia 1

Glycemic targets that must be achieved: 1, 2

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

HbA1c Monitoring

HbA1c has limited utility in GDM management but should be measured monthly if used: 1

• HbA1c decreases during normal pregnancy due to increased red cell turnover, making it less reliable than blood glucose monitoring 1
• Target HbA1c <6% (42 mmol/mol) 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 altered red cell turnover in pregnancy, measure monthly if used at all 1

Medical Nutrition Therapy (First-Line Treatment)

All women with GDM must receive nutritional counseling within the first week of diagnosis: 2

Mandatory minimum daily nutrient requirements: 2, 3

• Minimum 175g carbohydrate daily (never reduce below this threshold as it risks fetal growth compromise) 3
• Minimum 71g protein daily 2, 3
• Minimum 28g fiber daily 2, 3
• Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 2, 3

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

Carbohydrate distribution strategy: 3

• Spread carbohydrates across 3 small-to-moderate meals and 2-4 snacks throughout the day
• An evening snack is usually necessary to prevent accelerated ketosis overnight

Physical Activity

Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week, unless contraindicated: 2, 3

• Regular aerobic exercise lowers fasting and postprandial glucose and should be used as an adjunct to nutrition therapy 3
• Lifestyle modification (medical nutrition therapy + exercise) is sufficient for 70-85% of women with GDM 3

Pharmacologic Management

If glycemic targets are not achieved within 1-2 weeks of lifestyle modifications alone, initiate insulin therapy immediately as the first-line pharmacologic agent: 2, 4

Insulin is the preferred and recommended first-line medication because: 2, 4, 5

• It does not cross the placenta to a measurable extent 2, 5
• It has superior safety and efficacy profiles compared to oral agents 2

Avoid metformin and glyburide as first-line therapy due to their inferior outcomes and safety profiles compared to insulin 2

Fetal Surveillance

Ultrasound monitoring of fetal abdominal circumference should begin in the second and early third trimesters and be repeated every 2-4 weeks: 1

• Fetal abdominal circumference measurements provide useful information (in combination with maternal blood glucose levels) to guide management decisions 1
• Less intensified management may be allowed with normal growth (fetal abdominal circumference <75th percentile for gestational age), although some blood glucose monitoring should continue 1
• Lower targets for glycemic control or intensification of pharmacologic therapy should be considered when fetal abdominal circumference is excessive 1

Additional maternal surveillance: 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

Ketone Monitoring

Monitor for ketonuria with daily urine ketone testing if there is concern about inadequate caloric intake or excessive carbohydrate restriction: 3

• Ketonemia from starvation ketosis must be avoided 1, 3
• Fingerstick blood ketone testing is more representative of laboratory measurements of β-hydroxybutyrate than urine testing 1

Postpartum Follow-Up

All women with GDM must be tested for persistent diabetes or prediabetes at 4-12 weeks postpartum: 1, 2

• Use a 75-g oral glucose tolerance test (OGTT) with non-pregnancy diagnostic criteria 1, 2
• Do NOT use HbA1c at this visit because the concentration may still be influenced by changes during pregnancy and/or peripartum blood loss 1

Long-term surveillance is mandatory: 1

• 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 HbA1c, annual fasting plasma glucose, or triennial 75-g OGTT) 1

Timing and Route of Delivery

Delivery timing depends on glycemic control: 1

• For women with diet-controlled GDM meeting glycemic targets: delivery at 39-40 weeks of gestation is appropriate 1, 6
• For women requiring insulin or with poor glycemic control: delivery at 39 weeks of gestation is recommended 6
• There is no evidence supporting delivery before 38 weeks' gestation in the absence of objective evidence of maternal or fetal compromise 1
• Intensify fetal surveillance if pregnancy continues beyond 40 weeks' gestation 1