Hemoglobin A1C (Glycated Hemoglobin)
Hemoglobin A1C reflects average glycemia over the prior 8–12 weeks. During pregnancy, physiologic changes in red blood cell turnover can result in slightly lower values. HbA1C is useful for identifying overt diabetes but is not recommended as a standalone screening test for gestational diabetes.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| % | 4 – 6 | 4 – 6 | 4 – 6 | 4 – 7 |
| Proportion of Total Hgb | 0.04 – 0.06 | 0.04 – 0.06 | 0.04 – 0.06 | 0.04 – 0.07 |
Diagnostic note: An HbA1C ≥ 6.5% (DCCT/UKPDS standardized) is diagnostic of overt diabetes in pregnancy.
Causes of low hemoglobin A1C in pregnancy
- Recent blood loss or postpartum hemorrhage
- Hemolytic anemia (G6PD deficiency, autoimmune hemolysis)
- Hemoglobinopathies (sickle cell disease, thalassemia)
- Increased red blood cell turnover (shortened RBC lifespan in pregnancy)
- Chronic kidney disease with erythropoietin therapy
- Iron deficiency treatment causing rapid reticulocytosis
- Recent blood transfusion
Causes of high hemoglobin A1C in pregnancy
- Undiagnosed or poorly controlled diabetes
- Prediabetes
- Iron deficiency anemia (false elevation)
- Chronic kidney disease
- Glucocorticoid therapy
- Vitamin B12 or folate deficiency (reduced RBC turnover)
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Obstet Gynecol. 2009.
- IADPSG Consensus Panel. Diabetes Care. 2010.
- American Diabetes Association. Standards of Medical Care in Diabetes. 2024.
- Radin MS. Pitfalls in hemoglobin A1C measurement. J Gen Intern Med. 2014.
- Nielsen LR et al. Diabetes Care. 2006.