When should A1C (Hemoglobin A1C) testing be performed postpartum in women with a history of gestational diabetes?

A1C Testing in Postpartum Women with Gestational Diabetes

A1C testing should NOT be used for initial postpartum screening of women with gestational diabetes at 4-12 weeks postpartum; instead, a 75g oral glucose tolerance test (OGTT) using non-pregnancy criteria is the recommended test. 1

Initial Postpartum Testing Recommendations

• A 75g OGTT using non-pregnancy diagnostic criteria should be performed at 4-12 weeks postpartum in all women with a history of gestational diabetes mellitus (GDM) 1
• OGTT is specifically recommended over A1C at 4-12 weeks postpartum because A1C may be persistently impacted (lowered) by the increased red blood cell turnover related to pregnancy, blood loss at delivery, or by the preceding 3-month glucose profile 1
• The OGTT is more sensitive at detecting glucose intolerance, including both prediabetes and diabetes in the early postpartum period 1
• In the absence of unequivocal hyperglycemia, a positive screen for diabetes requires two abnormal values on the OGTT 1

Why A1C is Not Recommended for Initial Postpartum Testing

• A1C values are unreliable in the early postpartum period due to physiological changes during pregnancy and delivery 1
• Increased red blood cell turnover during pregnancy artificially lowers A1C values 1
• Blood loss at delivery further impacts A1C results, making them less reliable for diagnosis 1
• The preceding 3-month glucose profile (which includes the pregnancy period) affects A1C values, potentially masking postpartum dysglycemia 1

Long-term Follow-up Testing After Initial Postpartum Period

• After the initial 4-12 week postpartum OGTT, women with a history of GDM should have lifelong screening for diabetes every 1-3 years 1
• For ongoing evaluation after the initial postpartum period, any recommended glycemic test can be used, including: 1
  • Annual A1C testing 1
  • Annual fasting plasma glucose 1
  • Triennial 75g OGTT using non-pregnant thresholds 1

Clinical Considerations and Pitfalls

• Poor adherence to postpartum testing is common - studies show only about 50% of women return for the recommended 6-12 week postpartum OGTT 2
• Women with GDM have a significantly increased lifetime risk of developing type 2 diabetes (50-60% lifetime risk) 1
• Risk increases linearly over time: approximately 20% at 10 years, 30% at 20 years, 40% at 30 years, 50% at 40 years, and 60% at 50 years 1
• Women with prediabetes identified at postpartum testing should receive intensive lifestyle interventions and/or metformin to prevent progression to diabetes 1

Risk Factors for Postpartum Dysglycemia

• Family history of diabetes is independently associated with postpartum impaired glucose regulation 3
• Having all three glucose values exceeding diagnostic thresholds during pregnancy OGTT is associated with higher risk of postpartum dysglycemia 3
• Women who required insulin during pregnancy have higher rates of postpartum glucose abnormalities 3
• Prepregnancy BMI and weight gain after pregnancy are significant risk factors for developing type 2 diabetes 1

Remember that early detection of persistent diabetes or prediabetes after GDM is critical for implementing timely interventions to reduce long-term morbidity and mortality related to diabetes complications.