Insulin Therapy for Type 2 Diabetes in Pregnancy
Insulin is the preferred and first-line pharmacologic treatment for type 2 diabetes in pregnancy, as it does not cross the placenta and provides the safest option for both mother and fetus. 1
Initial Management Before Insulin
Before starting insulin, begin with medical nutrition therapy, physical activity, and weight management, with minimum daily requirements of 175g carbohydrate, 71g protein, and 28g fiber. 1 Target weight gain of 15-25 lb for overweight women and 10-20 lb for obese women—never recommend weight loss during pregnancy due to increased risk of small-for-gestational-age infants. 1
When to Initiate Insulin
Start insulin when lifestyle modifications fail to maintain glycemic targets or when signs of excessive fetal growth appear. 2 Glycemic control is often easier to achieve in type 2 diabetes than type 1 diabetes, but may require much higher insulin doses, sometimes necessitating concentrated insulin formulations. 3
Glycemic Targets
Achieve the following blood glucose goals through frequent monitoring (4-6 times daily): 1, 4
- Fasting glucose: 70-95 mg/dL
- One-hour postprandial: 110-140 mg/dL
- Two-hour postprandial: 100-120 mg/dL
- A1C target: <6% to <7% (42-53 mmol/mol), individualized to avoid hypoglycemia
Insulin Regimen and Dosing
Use multiple daily injections with a basal-bolus regimen or insulin pump technology. 1 Both delivery methods are acceptable, with neither demonstrating superiority over the other. 2
Expect insulin requirements to increase dramatically: Doses will approximately double by the third trimester, with linear increases of about 5% per week starting around 16 weeks gestation. 1 This differs from type 1 diabetes where requirements may initially decrease in the first trimester. 4
FDA-Approved Insulin Types
The FDA has approved insulin lispro, insulin aspart, and insulin detemir for use in pregnancy, with published studies showing no association with major birth defects, miscarriage, or adverse maternal or fetal outcomes. 2, 5 These rapid-acting analogs improve postprandial glucose control and are considered safe and effective. 6, 7
Role of Metformin (Not First-Line)
Metformin may be considered as adjunctive therapy to insulin only, not as monotherapy, due to lack of long-term safety data. 1 One randomized controlled trial found that adding metformin to insulin resulted in less maternal weight gain and fewer cesarean births and macrosomic neonates, but there was a doubling of small-for-gestational-age neonates. 3 The American Diabetes Association does not recommend metformin as first-line therapy due to concerns about long-term offspring safety and failure to provide adequate glycemic control in 25-28% of women. 2
Critical Safety Measures
Hypoglycemia Prevention
Provide comprehensive education to patients and family members on hypoglycemia prevention, recognition, and treatment before, during, and after pregnancy, as counter-regulatory responses are altered in pregnancy. 1, 4 Glucagon should be available and close contacts trained in its use. 8
Preeclampsia Prevention
Prescribe low-dose aspirin 100-150 mg daily (not the standard 81 mg, which is ineffective) starting at 12-16 weeks gestation to reduce preeclampsia risk. 3, 1, 2 A dosage of 162 mg/day may be suggested to reduce risk of uncontrolled maternal hypertension. 3
Medication Discontinuation
Immediately discontinue ACE inhibitors, angiotensin receptor blockers, and statins at conception due to fetal risks including renal dysplasia, oligohydramnios, pulmonary hypoplasia, and intrauterine growth restriction. 3, 1
Monitoring and Titration
Evaluate insulin requirements every 2-3 weeks as pregnancy progresses, with more frequent adjustments based on blood glucose patterns, carbohydrate intake, physical activity, and gestational age. 4, 2 Continuous glucose monitoring can improve glycemic control and reduce hypoglycemia risk. 2
Postpartum Management
After delivery, insulin requirements drop dramatically. 3 Reduce insulin to 50% of end-pregnancy doses or 80% of pre-pregnancy doses immediately after delivery, and monitor closely for hypoglycemia, especially during breastfeeding. 1
Specialized Care Referral
Refer to a specialized center offering team-based care (including maternal-fetal medicine specialist, endocrinologist experienced in managing pregnancy with preexisting diabetes, dietitian, nurse, and social worker) due to the complexity of insulin management in pregnancy. 3, 1, 4