When is Hemoglobin A1c (HbA1c) accurate after delivery in the postpartum period?

From the Guidelines

Hemoglobin A1c (HbA1c) testing is not accurate until at least 4-12 weeks postpartum, and even then, it may be persistently impacted by pregnancy-related factors, making the oral glucose tolerance test (OGTT) a more reliable option for detecting glucose intolerance. During pregnancy, red blood cell turnover increases and hemoglobin levels fluctuate, which can affect HbA1c measurements and make them less reliable 1. After delivery, the body needs time to return to its non-pregnant state and establish a new steady state of red blood cells with normal lifespan. Since HbA1c reflects average blood glucose levels over the previous 2-3 months, waiting 4-12 weeks ensures that the test is measuring glycemic control that occurred entirely in the postpartum period. For women who had gestational diabetes, this timing allows for appropriate screening for persistent diabetes or prediabetes. If earlier assessment of glycemic status is needed postpartum, alternative tests such as fasting plasma glucose or OGTT may be more appropriate, as they reflect current glycemic status rather than the average over previous months.

The most recent and highest quality study, published in 2023, recommends the OGTT over A1C at 4–12 weeks postpartum because A1C may be persistently impacted (lowered) by the increased red blood cell turnover related to pregnancy, by blood loss at delivery, or by the preceding 3-month glucose profile 1. This study suggests that the OGTT is more sensitive at detecting glucose intolerance, including both prediabetes and diabetes.

Some key points to consider when interpreting HbA1c results postpartum include:

• The impact of pregnancy-related factors on HbA1c measurements, such as increased red blood cell turnover and blood loss at delivery 1
• The need for alternative tests, such as OGTT or fasting plasma glucose, for earlier assessment of glycemic status postpartum
• The importance of screening for persistent diabetes or prediabetes in women who had gestational diabetes, and the recommended timing for this screening.

From the Research

Hemoglobin A1c Accuracy Postpartum

• The accuracy of hemoglobin A1c (HbA1c) after delivery postpartum is not directly addressed in the provided studies 2, 3, 4, 5, 6.
• However, the studies discuss the validity and accuracy of HbA1c in diagnosing diabetes and prediabetes in various populations.
• According to the studies, HbA1c has varying sensitivity and specificity in diagnosing diabetes, with sensitivity ranging from 41.9% to 64.5% and specificity ranging from 80% to 98.9% 3, 4, 6.
• The studies suggest that HbA1c may not be accurate for diagnosing diabetes in all individuals, particularly in those with impaired glucose tolerance or prediabetes 3, 4, 5, 6.
• The American College of Obstetricians and Gynecologists (ACOG) recommends that women with gestational diabetes mellitus (GDM) be screened for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75-g oral glucose tolerance test (OGTT) or HbA1c [2 is not relevant to this point, but other sources are].
• However, there are no research papers provided to assist in answering this question regarding the specific timing of when HbA1c is accurate after delivery postpartum.

Factors Affecting HbA1c Accuracy

• Several factors can affect the accuracy of HbA1c, including:
  • Hemoglobin variants or disorders 3
  • Red blood cell lifespan or disorders 3
  • Iron deficiency or other nutritional deficiencies 3
  • Certain medications or medical conditions 3
• These factors may impact the accuracy of HbA1c results, particularly in individuals with certain medical conditions or taking certain medications 3.