What are the criteria for diagnosis and management of gestational diabetes in a pregnant woman?

Diagnosis and Management of Gestational Diabetes

Diagnostic Criteria

Gestational diabetes is diagnosed using a 75g oral glucose tolerance test (OGTT) at 24-28 weeks gestation, 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. 1

Screening Approach

• All pregnant women without known diabetes should undergo screening at 24-28 weeks of gestation 1
• High-risk women (history of GDM, obesity, age >35 years, previous macrosomic infant >4500g, polycystic ovary syndrome, ethnic groups with increased diabetes risk) should be screened at the first prenatal visit using standard diagnostic criteria 2, 3
• Women found to have fasting glucose ≥126 mg/dL, random glucose ≥200 mg/dL, or HbA1c ≥6.5% before 20 weeks gestation have overt diabetes in pregnancy, not GDM, and require more intensive management 2, 3

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Management Algorithm

Step 1: Immediate Lifestyle Intervention (First-Line for All)

All women with GDM must begin with medical nutrition therapy, physical activity, and glucose self-monitoring immediately upon diagnosis—70-85% will achieve adequate control with lifestyle alone. 1

Medical Nutrition Therapy

• Work with a registered dietitian to develop an individualized meal plan 1
• Minimum daily intake: 175g carbohydrate, 71g protein, 28g fiber 1
• Distribute carbohydrates across three small-to-moderate meals and 2-4 snacks throughout the day 4
• Emphasize low glycemic index carbohydrates, monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats 1, 5
• Critical pitfall: Avoid excessive carbohydrate restriction—substituting fat for carbohydrate can worsen insulin resistance and promote ketosis 1

Physical Activity

• Moderate-intensity aerobic activity: 20-50 minutes per day, 2-7 days per week, if not contraindicated 4, 5
• Both aerobic and resistance training improve glycemic outcomes 6

Glucose Monitoring Targets

Strict glycemic targets must be achieved to reduce maternal and fetal complications:

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

Step 2: Pharmacologic Therapy Initiation

If glycemic targets are not met within 1-2 weeks of lifestyle intervention, insulin therapy must be initiated immediately—insulin is the first-line pharmacologic agent. 1, 4, 7

Insulin Therapy (Preferred First-Line)

• Initial total daily dose: 0.7-1.0 units/kg of current body weight (use approximately 0.8 units/kg in third trimester) 4
• Basal-bolus regimen: 40% as basal insulin (NPH or long-acting analogs), 60% as prandial insulin (regular or rapid-acting analogs) 4, 7
• Basal distribution: 2/3 in morning, 1/3 at night 4
• Prandial distribution: Before each main meal based on carbohydrate content 4
• Dose adjustments: Increase by 10-20% weekly or biweekly if targets not met—insulin resistance increases exponentially in third trimester requiring frequent titration 4, 7
• All insulins are pregnancy category B except glargine and glulisine (category C), but all are safer than oral agents due to lack of placental transfer 7

Alternative Agents (Not Recommended as First-Line)

• Metformin: Crosses the placenta and lacks long-term offspring safety data; associated with 25-28% failure rate requiring insulin rescue 1, 8
• Glyburide: Crosses the placenta (umbilical cord levels 50-70% of maternal), associated with higher rates of neonatal hypoglycemia and macrosomia compared to insulin 1
• Critical recommendation: Neither metformin nor glyburide should be used as first-line therapy—insulin remains the gold standard 1, 4, 7

Step 3: Monitoring and Adjustment

• Daily self-monitoring of fasting and postprandial glucose with food records 4
• Weekly or biweekly insulin dose adjustments in third trimester due to rapidly increasing insulin resistance 4, 7
• Monthly HbA1c monitoring (target <6% if achievable without hypoglycemia), though self-monitoring provides more actionable real-time data 7
• Ketone monitoring: Check fasting urine ketones to identify excessive carbohydrate restriction 1
• Hypoglycemia prevention: Include bedtime snack containing carbohydrates to prevent nocturnal hypoglycemia and accelerated ketosis 4

Step 4: Telehealth Integration

Telehealth visits for GDM improve outcomes compared to standard in-person care, reducing cesarean delivery, neonatal hypoglycemia, macrosomia, preeclampsia, and preterm birth. 1

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Maternal and Fetal Monitoring

• Regular obstetric examinations including ultrasound to assess fetal growth and amniotic fluid 2, 3
• Fetal surveillance for macrosomia, polyhydramnios, and other complications 1
• Women with diet-controlled GDM can await spontaneous labor; those requiring insulin therapy should have elective induction at term 8

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Postpartum Management

Immediate Postpartum (4-12 Weeks)

All women with GDM must undergo a 75g OGTT at 4-12 weeks postpartum using non-pregnancy diagnostic criteria to reclassify glucose tolerance. 1, 2, 3

• Insulin requirements drop dramatically after placental delivery—discontinue pregnancy-specific insulin regimens unless specific indication exists 6
• If diabetes persists postpartum, transition to standard diabetes management with metformin as first-line agent 6

Long-Term Follow-Up

• Lifelong screening for diabetes or prediabetes at least every 2-3 years 1, 2, 3
• Women with history of GDM have 50-70% risk of developing type 2 diabetes over 15-25 years 6
• Intensive lifestyle intervention or metformin for women with prediabetes reduces progression to diabetes by 35-40% over 10 years 1
• Counsel about increased risk of cardiovascular disease and metabolic syndrome 8

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Critical Pitfalls to Avoid

• Never delay insulin initiation beyond 1-2 weeks if lifestyle fails—this increases risks of macrosomia, shoulder dystocia, and cesarean delivery 7
• Never use fixed insulin doses—pregnancy physiology demands frequent adjustments, particularly in second and third trimesters when insulin resistance increases rapidly 7
• Never rely solely on HbA1c for management decisions—self-monitoring provides more actionable data for insulin adjustments 7
• Never continue pregnancy-specific insulin regimens postpartum without specific indication—transition to standard diabetes management 6
• Never use glyburide or metformin as first-line therapy—inferior efficacy, higher hypoglycemia risk, and placental transfer make insulin the safest choice 1, 6, 4
• Never assume women with only one elevated OGTT value need less aggressive monitoring—single elevated value identifies increased risk requiring full treatment 7