What is the recommended management for hyperglycemia in late pregnancy?

Management of Hyperglycemia in Late Pregnancy

Insulin is the first-line pharmacological treatment for hyperglycemia in late pregnancy, combined with medical nutrition therapy and glucose monitoring targeting fasting glucose <95 mg/dL and 1-hour postprandial <140 mg/dL. 1, 2

Initial Management Approach

Lifestyle Modifications First

• Begin with medical nutrition therapy and physical activity as 70-85% of women with gestational diabetes can achieve glycemic control through lifestyle changes alone 1, 3
• Refer to a registered dietitian to establish an individualized food plan providing minimum 175g carbohydrate daily, 71g protein daily, and 28g fiber daily 1, 3
• Recommend at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 3

Glucose Monitoring Targets

The American Diabetes Association and ACOG recommend the following specific targets 1, 2:

• Fasting glucose: <95 mg/dL (5.3 mmol/L)
• 1-hour postprandial: <140 mg/dL (7.8 mmol/L)
• 2-hour postprandial: <120 mg/dL (6.7 mmol/L)

Monitor fasting and postprandial glucose levels, as postprandial monitoring is associated with better glycemic control and lower risk of preeclampsia 1

Pharmacological Treatment

When to Initiate Insulin

• Add insulin if glycemic targets are not achieved with lifestyle modifications alone 1, 3
• Women with greater initial degrees of hyperglycemia may require earlier initiation of pharmacological therapy 3

Why Insulin is Preferred

• Insulin does not cross the placenta to a measurable extent, making it the safest option for the fetus 1, 2
• All insulins are pregnancy category B except glargine and glulisine (category C) 1
• Insulin requirements increase exponentially during the second trimester and level off toward the end of the third trimester 1

Oral Agents: Not Recommended as First-Line

Metformin and glyburide should NOT be used as first-line agents 1, 3:

• Metformin crosses the placenta, resulting in umbilical cord blood levels as high or higher than maternal levels 1

• The MiG TOFU study showed 9-year-old offspring exposed to metformin were heavier with higher waist-to-height ratios than those exposed to insulin 1

• Metformin fails to provide adequate glycemic control in 25-28% of women with GDM 1, 3

• Glyburide crosses the placenta with umbilical cord concentrations 50-70% of maternal levels 1

• Glyburide was associated with higher rates of neonatal hypoglycemia and macrosomia than insulin in meta-analyses 1

• Glyburide fails to provide adequate glycemic control in 23% of women with GDM 1, 3

A1C Targets in Late Pregnancy

• Target A1C <6% (42 mmol/mol) if achievable without significant hypoglycemia 1, 2
• A1C levels fall during pregnancy due to increased red blood cell turnover, so it should be used as a secondary measure after self-monitoring of blood glucose 1
• Monitor A1C monthly during pregnancy given altered red blood cell kinetics 1

Insulin Dosing Considerations in Late Pregnancy

• Insulin requirements increase linearly by approximately 5% per week through week 36 1
• This typically results in doubling of daily insulin dose compared to prepregnancy requirements 1
• A rapid reduction in insulin requirements can indicate placental insufficiency and requires immediate evaluation 1
• Insulin requirements level off toward the end of the third trimester with placental aging 1

Common Pitfalls to Avoid

• Do not delay insulin initiation when lifestyle modifications fail to achieve targets, as this increases risk of macrosomia and birth complications 1, 3
• Do not rely solely on A1C for glycemic control assessment, as it may not capture postprandial hyperglycemia that drives macrosomia 1
• Do not use metformin or glyburide as first-line agents despite their convenience, given placental transfer and long-term safety concerns 1, 3
• Monitor for hypoglycemia carefully when intensifying insulin therapy, as hypoglycemia may increase risk of low birth weight 1

Additional Management Considerations

• Prescribe low-dose aspirin (60-150 mg/day) if not already initiated to reduce preeclampsia risk in women with preexisting diabetes 2
• Monitor for diabetic retinopathy progression if present, as rapid implementation of euglycemia can worsen retinopathy 2
• Plan for dramatic decrease in insulin requirements immediately after delivery of the placenta 2