How should I adjust the insulin regimen for a 24‑week pregnant woman on insulin glargine (Lantus) 17 U nightly with acceptable fasting glucose but 1‑hour post‑prandial glucose of 188 and 158 mg/dL and a carbohydrate‑to‑insulin ratio of 1 U per 6 g?

Increase Prandial Insulin to Target Postprandial Excursions

Your patient's fasting glucose is acceptable at 122 mg/dL, but her 1-hour postprandial values of 188 and 158 mg/dL exceed the ADA target of 110–140 mg/dL; you should immediately increase her rapid-acting prandial insulin doses rather than adjust basal insulin. 1, 2

Why Prandial Insulin Needs Adjustment

• The 1-hour postprandial target during pregnancy is 110–140 mg/dL, and your patient's values of 188 and 158 mg/dL are significantly above this threshold. 1, 2

• Her fasting glucose of 122 mg/dL falls within the acceptable range of 70–95 mg/dL (though at the upper end), indicating that basal insulin glargine 17 units is providing adequate overnight coverage. 1, 2

• Basal insulin alone does not control postprandial excursions; rapid-acting insulin (lispro or aspart) before each meal is required to address meal-related glucose spikes. 2

Specific Prandial Insulin Adjustment Algorithm

• Increase her carbohydrate-to-insulin ratio from 1 unit per 6 grams to 1 unit per 5 grams (a 20% increase in prandial insulin) for the meals where postprandial glucose exceeds 140 mg/dL. 2

• Titrate every 2–3 days by further tightening the ratio (e.g., 1:4.5, then 1:4) until 1-hour postprandial values consistently fall below 140 mg/dL. 2

• At 24 weeks gestation, she is entering the phase of exponentially rising insulin resistance (weeks 17–36), during which insulin requirements typically increase by approximately 5% per week and may double or triple by week 36. 1, 2

Monitoring Requirements

• Perform self-monitoring of blood glucose 4–6 times daily: fasting, before each meal (preprandial), and 1 hour after each meal. 1, 2

• The 2-hour postprandial target is 100–120 mg/dL if you choose to monitor at 2 hours instead of 1 hour. 1, 2

• Check A1C monthly with a target < 6% if achievable without significant hypoglycemia, or relax to < 7% if hypoglycemia becomes problematic. 1, 2

When to Adjust Basal Insulin

• Only increase basal insulin glargine if fasting glucose rises above 95 mg/dL on consecutive days. 2

• If fasting glucose exceeds 95 mg/dL, increase glargine by 2–4 units every 2–3 days until fasting values consistently fall below 95 mg/dL. 2

• Given her current fasting glucose of 122 mg/dL, a modest basal increase of 2–3 units (to 19–20 units) may be warranted to bring fasting glucose closer to the lower end of the target range, but prandial insulin adjustment is the priority. 2

Critical Safety Considerations

• Comprehensive hypoglycemia education for the patient and family is mandatory, as pregnancy attenuates counter-regulatory hormone responses and increases hypoglycemia risk, especially in the first trimester. 1, 2

• A sudden unexplained drop in insulin requirements may signal placental insufficiency and requires immediate obstetric evaluation. 1, 2

• Insulin glargine is acceptable during pregnancy despite limited randomized trial data, particularly for women already well-controlled on this regimen pre-pregnancy. 2, 3, 4

Multidisciplinary Referral

• Referral to a specialized diabetes-and-pregnancy center with coordinated maternal-fetal medicine, endocrinology, diabetes education, and nutrition support is strongly recommended to manage the complex insulin adjustments required during pregnancy. 2, 5