What about the other laboratory tests in managing hyperglycemia in pregnancy?

Laboratory Tests for Managing Hyperglycemia in Pregnancy

For comprehensive management of hyperglycemia in pregnancy, blood glucose monitoring should be the primary laboratory test, with specific targets of fasting glucose <95 mg/dL, 1-hour postprandial glucose <140 mg/dL, or 2-hour postprandial glucose <120 mg/dL. 1

Key Laboratory Tests for Monitoring

Blood Glucose Monitoring

• Blood glucose monitoring remains the cornerstone of hyperglycemia management in pregnancy, with specific targets established by the Fifth International Workshop-Conference on Gestational Diabetes Mellitus 1
• For women with gestational diabetes mellitus (GDM), both fasting and postprandial glucose measurements are essential due to the unique glucose homeostasis in pregnancy 1
• Venous plasma or serum glucose should be measured using enzymatic methods with high accuracy and precision, with proper sample collection and processing to minimize pre-analytic glycolysis 1
• Capillary and venous plasma glucose concentrations differ and are not interchangeable 1

HbA1c Testing

• HbA1c should be measured monthly during pregnancy due to altered red cell turnover 1
• HbA1c target <6% (42 mmol/mol) is optimal in pregnancy if it can be achieved without significant hypoglycemia 1
• HbA1c should not replace blood glucose monitoring as it may not adequately detect postprandial hyperglycemia, which is primarily responsible for macrosomia 1
• HbA1c values decrease during normal pregnancy due to increased red cell turnover, which must be considered when interpreting results 1

Continuous Glucose Monitoring (CGM)

• CGM provides actionable data to address fasting and postprandial hypoglycemia or hyperglycemia in pregnancies complicated by type 1 diabetes 1
• For pregnant women with type 1 diabetes using CGM, target ranges should be 63–140 mg/dL (3.5–7.8 mmol/L) for >70% of time 1
• There are insufficient data to support the use of CGM in people with type 2 diabetes or GDM 1

Postpartum Testing

• Women with GDM should undergo a 75-g oral glucose tolerance test (OGTT) at 4-12 weeks postpartum using non-pregnant criteria to detect persistent hyperglycemia 1
• HbA1c is not recommended for immediate postpartum evaluation as it may be influenced by pregnancy-related changes and peripartum blood loss 1
• Lifelong screening for diabetes should be performed in women with history of GDM using standard non-pregnant criteria at least every 3 years 1
• Options for long-term follow-up include annual HbA1c, annual fasting plasma glucose, or triennial 75-g OGTT (with non-pregnant cutoffs) 1

Early Detection of GDM

• There is ongoing research but insufficient evidence to recommend testing for GDM before 20 weeks of gestation 1
• HbA1c at the first prenatal visit identifies risk of adverse pregnancy outcomes but is less effective for ascertainment of GDM 1
• Other biomarkers such as CD59 or serum secreted frizzle-related protein-5 may be useful in early identification of women who will develop GDM later in pregnancy 1

Tests Not Recommended

• Urine glucose testing is not recommended for routine care of patients with diabetes mellitus during pregnancy 1
• Capillary glucose measurements should not be used for diagnostic purposes due to their lack of precision compared to venous plasma measurements 1

Special Considerations

• In individuals with disorders affecting red blood cell turnover, HbA1c measurements may provide spurious (generally falsely low) results, necessitating alternative glucose testing methods 1
• Alternative glycated protein assays (fructosamine or glycated albumin) may be used when abnormalities in red blood cell turnover, hemoglobin variants, or other interfering factors compromise HbA1c interpretation 1
• Laboratories should be aware of potential interferences, including hemoglobin variants that may affect HbA1c test results depending on the method used 1

Clinical Implications

• The 1-hour glucose value during OGTT in pregnancy may be a valuable prediction tool for identifying women at high risk of future type 2 diabetes and cardiovascular disease 2
• Maternal hyperglycemia is associated with both short-term pregnancy complications and long-term health implications for mother and offspring 3
• Proper laboratory testing and management of hyperglycemia in pregnancy can reduce the risk of macrosomia and other adverse outcomes 1