A 32-year-old multiparous woman from Mumbai is diagnosed with gestational diabetes at 26 weeks gestation. She has been on medical nutrition therapy for 2 weeks with home glucose monitoring. Her fasting glucose readings are consistently 110–125 mg/dL and 2-hour postprandial readings are 155–175 mg/dL, both above target. She is overweight (BMI 28 kg/m²) and has no contraindications to insulin or metformin. What is the most appropriate next step?

Explanation

## Pharmacotherapy Initiation in GDM: Insulin as First-Line **Key Point:** After 2 weeks of MNT failure to achieve glycemic targets, insulin therapy is indicated and is the preferred first-line pharmacological agent in pregnancy. ### Glycemic Targets in GDM | Measurement | Target (mg/dL) | |---|---| | Fasting | <95 | | 1-hour postprandial | <140 | | 2-hour postprandial | <120 | **Clinical Pearl:** This patient's readings (fasting 110–125, postprandial 155–175) exceed all targets, indicating MNT failure. Pharmacotherapy is now indicated. ### Insulin vs. Metformin in Pregnancy | Feature | Insulin | Metformin | |---|---|---| | **Placental transfer** | Minimal (large molecule) | Crosses placenta | | **Fetal safety** | Excellent; no teratogenicity | Generally safe; less evidence | | **Maternal hypoglycemia risk** | Yes; requires patient education | Minimal | | **First-line in pregnancy** | ✓ YES | Second-line; if insulin declined | | **Efficacy** | Rapid; dose-titrable | Moderate; slower onset | | **GI side effects** | None | Nausea, diarrhea (10–30%) | **High-Yield:** Insulin is the gold standard in pregnancy because it does not cross the placenta and has decades of safety data. Metformin is a reasonable alternative if the patient refuses insulin, but it is NOT first-line. ### Insulin Regimens in GDM 1. **Basal-bolus (preferred)** - Long-acting basal: NPH at bedtime or long-acting analog (glargine, detemir) - Rapid-acting bolus: Aspart or lispro before meals - Allows flexible meal timing and better glycemic control 2. **Premixed insulin** - Less flexible; fixed carbohydrate intake required **Mnemonic:** **INSULIN FIRST** in GDM pregnancy — **I**nsulin is safest, **N**o placental transfer, **S**ulin has decades of safety, **U**nlike metformin which crosses, **L**ong-acting basal + rapid bolus, **I**mmediately effective, **N**eed dose titration, **F**etal safety paramount, **I**ncrease doses as pregnancy progresses, **R**apid-acting for meals, **S**tart low, titrate up, **T**arget fasting <95, postprandial <120. ### Dose Initiation - **Starting dose:** 0.7–1.0 IU/kg/day divided as 50% basal, 50% bolus - **Titration:** Increase by 2–4 IU every 3 days based on glucose readings - **Insulin requirement increases** as pregnancy advances (up to 2–3× by third trimester) **Warning:** Do NOT continue MNT alone beyond 2 weeks if targets are unmet; this delays fetal benefit and increases maternal/fetal complications.