What insulin regimen is recommended for a pregnant woman with gestational diabetes who cannot achieve fasting glucose <95 mg/dL and 1‑hour post‑prandial glucose <140 mg/dL with diet and exercise?

Insulin Regimen for Gestational Diabetes

Start insulin immediately when fasting glucose remains ≥95 mg/dL or 1-hour postprandial ≥140 mg/dL despite 1–2 weeks of medical nutrition therapy and exercise. 1, 2

Initial Insulin Regimen

Calculate the total daily insulin dose as 0.5 units/kg of current body weight, divided into 50% basal insulin and 50% prandial insulin distributed across three meals. 2 This physiologic basal-bolus approach mimics endogenous insulin secretion and achieves tighter glycemic control while reducing hypoglycemia risk. 3

Preferred Insulin Types

• Rapid-acting prandial insulin: Use insulin lispro or insulin aspart before each meal, as both have been studied in randomized controlled trials and demonstrate pregnancy safety. 2
• Basal insulin: Use insulin detemir or NPH insulin for overnight and between-meal coverage. 2 NPH remains an acceptable alternative, particularly when cost is a concern. 2
• Insulin glargine: Can be considered acceptable for women already well-controlled on this regimen pre-pregnancy, despite limited randomized trial data. 2

Glycemic Targets for Titration

Monitor blood glucose 4–6 times daily (fasting and after each meal) to guide dose adjustments. 2 Target the following values:

• Fasting: 70–95 mg/dL 2, 4
• 1-hour postprandial: 110–140 mg/dL 2, 4
• 2-hour postprandial: 100–120 mg/dL 2, 4

The lower fasting limit of 70 mg/dL applies only to insulin-treated patients to prevent hypoglycemia. 2

Dose Titration Strategy

Adjust insulin doses every 2–3 days based on glucose patterns:

• For elevated fasting glucose: Increase basal insulin by 2–4 units every 2–3 days until fasting values consistently fall below 95 mg/dL. 2
• For elevated postprandial glucose: Increase the corresponding pre-meal rapid-acting insulin by approximately 20% (e.g., tighten the carbohydrate-to-insulin ratio from 1:6 to 1:5), then continue titrating every 2–3 days until postprandial values meet targets. 2

Insulin requirements rise exponentially during pregnancy: Expect a 2–3-fold increase in total daily dose during the second and third trimesters (weeks 17–36), with requirements typically rising approximately 5% per week through week 36. 2 This necessitates weekly or bi-weekly dose escalations. 2

A1C Monitoring

Measure A1C monthly, targeting <6% (42 mmol/mol) if achievable without significant hypoglycemia; relax to <7% (53 mmol/mol) if hypoglycemia risk is high. 2, 4 Pregnancy increases red blood cell turnover, physiologically lowering A1C, so treat it as a secondary metric—it may miss postprandial spikes that drive macrosomia. 2, 4

Critical Safety Considerations

Provide comprehensive hypoglycemia education to the patient and family before initiating insulin. 2 First-trimester hypoglycemia risk is highest due to increased insulin sensitivity. 2, 4 Pregnancy attenuates counter-regulatory hormone responses, reducing hypoglycemia awareness. 2

An abrupt, unexplained drop in insulin requirements may indicate placental insufficiency and requires immediate obstetric evaluation. 2 This is a red-flag situation that cannot be ignored.

Postpartum Insulin Management

Insulin requirements drop precipitously after placental delivery. Resume insulin at either 80% of pre-pregnancy doses or 50% of end-of-pregnancy doses immediately postpartum to prevent severe hypoglycemia. 2 Close monitoring is required for the first 48 hours. 2

For women with gestational diabetes (not pre-existing diabetes), stop insulin after delivery and check blood glucose before meals and 2 hours after meals for 48 hours. 2

Multidisciplinary Care

Refer to a specialized diabetes-and-pregnancy center offering team-based care (maternal-fetal medicine, endocrinology, diabetes education, nutrition) for optimal maternal and fetal outcomes. 2 The complexity of insulin management in pregnancy—with rapidly changing requirements and narrow therapeutic windows—makes specialized care essential rather than optional.

Common Pitfalls to Avoid

• Do not use premixed insulin (e.g., NovoMix) in pregnancy; it does not permit the flexible dose adjustments required as insulin needs change rapidly throughout gestation. 2
• Do not allocate equal proportions to basal and prandial insulin throughout pregnancy; as pregnancy progresses, a greater proportion of total daily insulin should be allocated to prandial doses and a smaller proportion to basal insulin. 2
• Do not delay insulin initiation when 1–2 glucose values exceed targets over a 1–2 week period; the majority of randomized controlled trials (87%) used these tight criteria for starting pharmacologic treatment. 5
• Do not rely solely on A1C for management decisions, as macrosomia results primarily from postprandial hyperglycemia, which A1C may not adequately detect. 6