What are the guidelines for insulin therapy in pregnant women diagnosed with Gestational Diabetes Mellitus (GDM)?

Insulin Guidelines for Gestational Diabetes Mellitus

Insulin is the preferred first-line pharmacologic agent for GDM when lifestyle modifications (medical nutrition therapy and exercise) fail to achieve glycemic targets within 1-2 weeks. 1, 2

Initial Management Approach

Start with lifestyle modifications first - approximately 70-85% of women with GDM can achieve adequate glycemic control through medical nutrition therapy, exercise, and glucose monitoring alone, making insulin unnecessary for the majority. 1, 2

Glycemic Targets for Treatment Decisions

Monitor blood glucose levels and initiate insulin if targets cannot be maintained:

• Fasting glucose: <95 mg/dL 3, 2, 4
• 1-hour postprandial: <140 mg/dL 3, 2, 4
• 2-hour postprandial: <120 mg/dL 1, 3, 2

Alternative targets from ACOG if hypoglycemia occurs with stricter goals:

• Fasting <90 mg/dL, preprandial <105 mg/dL, 1-hour postprandial <130-140 mg/dL, 2-hour postprandial <120 mg/dL 1

Insulin Initiation and Dosing

When to start insulin: If blood glucose levels exceed targets despite 1-2 weeks of lifestyle modifications, insulin therapy should be initiated immediately. 2, 5

Insulin Regimen Structure

Use a basal-bolus regimen with a greater proportion as prandial insulin and smaller proportion as basal insulin. 1 This reflects the physiology of GDM, where postprandial hyperglycemia is the primary concern due to placental hormone-induced insulin resistance.

Dose Titration Requirements

Expect weekly or biweekly insulin dose increases during the second trimester due to rapidly increasing insulin resistance from diabetogenic placental hormones. 1 Insulin requirements increase exponentially during the second trimester and plateau toward the end of the third trimester. 1

Insulin Safety Profile

All insulins are pregnancy category B except glargine and glulisine (category C). 1 Despite this classification difference, insulin remains the preferred agent over oral medications due to lack of long-term safety data for noninsulin agents in pregnancy. 1

Monitoring Requirements

• Self-monitoring of blood glucose 4-7 times daily (fasting and postprandial measurements) 3
• A1C target: <6% if achievable without hypoglycemia 1
• Monthly A1C monitoring due to altered red blood cell kinetics during pregnancy 1, 3
• A1C should be used as a secondary measure alongside self-monitoring, as it may not fully capture physiologically relevant glycemic parameters in pregnancy 1

Referral Considerations

Referral to a specialized center is recommended if available due to the complexity of insulin management in pregnancy, including frequent titration needs and changing insulin requirements across trimesters. 1

Common Pitfalls to Avoid

• Do not delay insulin initiation if lifestyle modifications fail after 1-2 weeks - prolonged hyperglycemia increases risks of macrosomia, birth complications, shoulder dystocia, and neonatal hypoglycemia 2, 5
• Do not use fixed insulin doses - pregnancy physiology demands frequent adjustments, particularly during the second trimester when insulin resistance increases rapidly 1
• Do not rely solely on A1C for glucose management decisions - self-monitoring of blood glucose provides more actionable real-time data for insulin adjustments 1

Postpartum Management

Insulin resistance typically resolves immediately after delivery. 5 Women with GDM require reevaluation with a 75g oral glucose tolerance test at 4-12 weeks postpartum, then ongoing diabetes screening every 1-3 years due to significantly increased risk of developing type 2 diabetes. 1, 2, 4