Why is normalizing maternal glucose levels during labor problematic?

Normalizing Maternal Glucose During Labor: Risks and Considerations

Overzealous normalization of maternal glucose during labor can increase the risk of maternal hypoglycemia and potential fetal compromise, and should be avoided in favor of maintaining glucose levels between 5-10 mmol/L (90-180 mg/dL) during labor and delivery. 1

Physiological Changes During Labor

Labor represents a form of exercise that naturally lowers blood glucose levels. This creates a unique metabolic situation where:

• Labor has a glucose-lowering effect on maternal metabolism 2
• Insulin requirements typically decrease during active labor
• Maternal hypoglycemia can lead to maternal ketosis due to prolonged starvation during labor 2

Risks of Normalizing Glucose Too Aggressively

Maternal Risks:

• Increased risk of severe hypoglycemia requiring assistance from another person 3
• Potential for ketosis due to prolonged starvation during labor 2
• Cognitive impairment during a critical time when maternal participation may be needed

Fetal/Neonatal Risks:

• Fetal hypoglycemia and hypoinsulinism may result from maternal hypoglycemia 3
• Potential for intrauterine growth restriction with overzealous glycemic control 3
• Altered fetal heart rate patterns and increased fetal movements during maternal hypoglycemia 4

Optimal Glucose Targets During Labor

The ideal target range during labor and delivery should balance preventing neonatal hypoglycemia while avoiding maternal hypoglycemia:

• Target blood glucose: 5-10 mmol/L (90-180 mg/dL) during labor and delivery 1
• This more permissive range is safer than strict normalization to 4-6 mmol/L (72-108 mg/dL)
• For women with gestational diabetes who required minimal insulin (<1.0 units/kg/day), monitoring without IV insulin may be sufficient 5

Evidence Supporting More Permissive Targets

Research shows that while maternal hyperglycemia during labor is directly related to neonatal hypoglycemia 2, overly aggressive glucose control carries its own risks:

• Up to 40% of women with Type 1 diabetes report at least one episode of severe hypoglycemia during pregnancy 3
• Recent studies question whether tight glycemic control (4-7 mmol/L) is necessary for all women with diabetes in labor 6
• The risk-benefit ratio may not favor strict normalization, especially for women with well-controlled gestational diabetes

Management Recommendations

1. For insulin-dependent gestational diabetes:

   • No additional insulin is typically needed with onset of labor 2
   • Provide glucose-containing fluids at a rate of 2.55 mg/kg per minute once active labor is established 2

2. For type 1 diabetes:

   • Consider IV insulin with glucose monitoring during labor
   • Monitor potassium levels when administering IV insulin due to risk of hypokalemia 7

3. For all types of diabetes:

   • Begin with isotonic saline or electrolyte solutions
   • Switch to glucose-containing fluids once active labor is achieved 2
   • Monitor glucose levels regularly, with frequency determined by diabetes type and severity

Key Considerations for Clinical Practice

• Neonatal hypoglycemia is directly related to maternal hyperglycemia during labor, not to mild maternal hyperglycemia 2
• The ideal target glucose during labor has not been definitively established in guidelines 8
• Recent evidence suggests a more permissive approach may be appropriate, especially for well-controlled gestational diabetes 6
• Maternal hypoglycemia can be as concerning as hyperglycemia during this critical period

By maintaining glucose levels in the 5-10 mmol/L range rather than striving for strict normalization, clinicians can balance the risks of both maternal hypoglycemia and neonatal complications.