When is Hemoglobin A1c (HbA1c) accurate after childbirth?

From the Guidelines

Hemoglobin A1c testing is not accurate until at least 4-12 weeks postpartum due to physiological changes during pregnancy and childbirth. During pregnancy and the immediate postpartum period, hemoglobin A1c values may be affected by several physiological changes including increased red blood cell turnover, blood loss during delivery, and potential anemia, as noted in the 2023 standards of care in diabetes 1. These factors can artificially lower A1c readings, making them less reliable for diabetes diagnosis or monitoring.

Key Considerations

• The OGTT is recommended over A1C at 4–12 weeks postpartum because A1C may be persistently impacted by the increased red blood cell turnover related to pregnancy, by blood loss at delivery, or by the preceding 3-month glucose profile 1.
• For women who had gestational diabetes, it's recommended to use the OGTT for diabetes screening at 4-12 weeks postpartum, as it is more sensitive at detecting glucose intolerance, including both prediabetes and diabetes 1.
• Ongoing evaluation may be performed with any recommended glycemic test, such as annual A1C, annual fasting plasma glucose, or triennial 75-g OGTT using nonpregnant thresholds 1.

Clinical Implications

• Hemoglobin A1c reflects average blood glucose levels over the lifespan of red blood cells (approximately 120 days), so it takes time for the test to reflect the true post-pregnancy glycemic status once the body has returned to its non-pregnant state.
• In the interim period, other tests such as fasting plasma glucose or oral glucose tolerance tests may provide more accurate assessments of glycemic status.
• Individuals with a history of gestational diabetes should be tested every 1–3 years thereafter if the 4–12 weeks postpartum 75-g OGTT is normal, due to the increased lifetime maternal risk for diabetes estimated at 50–60% 1.

From the Research

Hemoglobin A1c Accuracy After Childbirth

• The accuracy of hemoglobin A1c (HbA1c) measurements can be affected by various factors, including changes in erythrocyte turnover and analytical interference 2.
• HbA1c reflects the glycaemic status of the latest 2-3 months and is used in both diagnosing and monitoring diabetes 2.
• Iron deficiency anemia (IDA) is a common cause of anemia worldwide and can affect HbA1c levels, with studies showing that IDA can increase HbA1c levels in both diabetic and non-diabetic patients 3, 4, 5, 6.
• Treatment of IDA with iron supplementation can decrease HbA1c levels in anemic patients with IDA and type 2 diabetes mellitus (T2DM) 4.
• Iron status should be considered during the interpretation of HbA1c concentrations in diabetes mellitus, and iron replacement therapy can decrease HbA1c in anemic patients with IDA and T2DM 4, 5.
• The mechanism of the association between increased levels of HbA1c and IDA is unclear, but hematological changes, iron metabolism, and other factors could affect the results of diagnostic investigations, leading to false results 6.
• There is no specific information available on when HbA1c is accurate after childbirth, as the provided studies do not address this topic directly.