How do you start and titrate insulin in patients with Gestational Diabetes Mellitus (GDM)?

Starting and Titrating Insulin in Gestational Diabetes Mellitus

Insulin should be initiated when medical nutrition therapy fails to maintain fasting plasma glucose <95 mg/dL, 1-hour postprandial <140 mg/dL, or 2-hour postprandial <120 mg/dL. 1

Indications for Insulin Initiation

Start insulin when lifestyle modifications (diet and exercise) fail to achieve glycemic targets within 1-2 weeks. 1 The specific thresholds are:

• Fasting plasma glucose ≥95 mg/dL 1
• 1-hour postprandial ≥140 mg/dL 1
• 2-hour postprandial ≥120 mg/dL 1

Women with marked hyperglycemia at diagnosis (fasting >110 mg/dL) or those showing signs of excessive fetal growth on ultrasound should receive insulin earlier, potentially bypassing the lifestyle-only phase. 1, 2

Choice of Insulin Regimen

Begin with a basal-bolus regimen using human insulin (NPH as basal, regular insulin as bolus) as first-line therapy. 2 This remains the standard approach with the most safety data in pregnancy. 1

Rapid-acting insulin analogs (lispro or aspart) may be used as alternatives to regular insulin for prandial coverage. 3, 2 These are FDA pregnancy category B and offer more physiologic postprandial control with potentially less hypoglycemia risk. 1

Insulin detemir is an acceptable basal insulin alternative to NPH. 3 Note that insulin glargine and glulisine are pregnancy category C, though existing studies show no clear contraindications. 1, 3

Starting Doses

For elevated fasting glucose (≥95 mg/dL): Start intermediate-acting insulin (NPH) at bedtime, 0.2 units/kg of actual body weight. 2, 4

For elevated postprandial glucose only: Start rapid-acting or regular insulin before the meal(s) with highest glucose excursions, beginning at 4 units per meal. 4 Alternatively, calculate 0.1 units/kg divided among meals. 4

For both fasting and postprandial elevations: Use a basal-bolus regimen with total daily dose of 0.7-1.0 units/kg in second trimester, increasing to 0.8-1.2 units/kg in third trimester. 4 Distribute as 40-50% basal insulin and 50-60% as prandial insulin divided among three meals. 1, 4

Titration Protocol

Adjust basal insulin based on fasting glucose values:

• If fasting glucose remains ≥95 mg/dL, increase bedtime NPH by 2-4 units every 3 days until target is achieved. 2, 4
• If fasting glucose <70 mg/dL, decrease basal insulin by 10-20%. 4

Adjust prandial insulin based on postprandial glucose values:

• If 1-hour postprandial ≥140 mg/dL or 2-hour postprandial ≥120 mg/dL, increase pre-meal insulin by 1-2 units every 3 days. 2, 4
• Target incremental increases of 10-15% of the current dose. 4

Insulin requirements increase weekly or biweekly during the second trimester due to rapidly rising insulin resistance. 1 Expect to double or triple insulin doses from early to late pregnancy. 1

Monitor and adjust insulin doses at least weekly during active titration, then every 1-2 weeks once stable. 4

Critical Monitoring Requirements

Perform self-monitoring of blood glucose 4-7 times daily: fasting and either 1-hour or 2-hour after each meal. 1 Postprandial monitoring is superior to preprandial monitoring for insulin-treated GDM. 1

Check A1C monthly during pregnancy as a secondary measure, targeting <6% without hypoglycemia. 1 However, A1C should not replace daily glucose monitoring as the primary assessment tool. 1

Common Pitfalls to Avoid

Do not delay insulin initiation beyond 1-2 weeks of failed lifestyle therapy. Early treatment prevents macrosomia and reduces perinatal complications. 1

Do not use fixed insulin doses throughout pregnancy. Insulin resistance increases exponentially in the second trimester, requiring frequent dose adjustments. 1

Do not stop basal insulin in type 1 diabetics during labor or postpartum. This creates high risk for diabetic ketoacidosis. 1

Avoid using insulin glargine or glulisine as first-line agents given their pregnancy category C designation, despite limited evidence of harm. 1

Intrapartum and Postpartum Management

During labor, switch to intravenous insulin infusion (0.5-2 units/hour) with hourly glucose monitoring, targeting 70-110 mg/dL. 1, 2 Women requiring <20 units total daily dose before labor may not need insulin infusion. 2

Stop all insulin immediately after delivery for women with GDM. 1, 2 Continue capillary glucose monitoring for 24-48 hours postpartum. 1, 2

For preexisting diabetes, reduce insulin to 50-80% of pre-pregnancy doses or 50% of late pregnancy doses immediately postpartum. 1

Referral Considerations

Refer to a specialized diabetes in pregnancy center when available, given the complexity of insulin management requiring weekly dose adjustments. 1 Team-based care with maternal-fetal medicine, endocrinology, and diabetes education improves outcomes. 1