Glycosylated hemoglobin (HbA1c) in the first trimester of pregnancy

Introduction: Glycosylated hemoglobin (HbA1c) is a form of hemoglobin that characterises a patient's plasma glucose over a prolonged period of time. The American Diabetic Association (ADA) supported the use of HbA1c as an option for the diagnosis of diabetes. A value of ≥6.5% was proposed as the criterion for diagnosis. A partial aim of our study was to assess if a first trimester HbA1c value of 5.7 – 6.4% (prediabetes) could be an early predictor of progression to gestational diabetes mellitus (GDM).

Methods: This is a prospective cohort study performed on all women who delivered at a single institution over 1.5 years and had an early HbA1c test performed in the first trimester. The primary outcome was the diagnosis of GDM. The prevalence of GDM in women with a first trimester HbA1c value of 5.7 – 6.4% was compared with that of women with an HbA1c < 5.7%. Continuous variables were analysed by unpaired Student's t -test or Mann-Whitney U-test. Proportions were analysed using Chi² test. Statistical significance was considered when p-value < 0.05.

Results: There were 280 women who met inclusion criteria during the study period: 263 of them had an HbA1c level of < 5.7% (group 1), and 17 (7.4%, group 2) between 5.7 and 6.4%. The prevalence of GDM in the entire study population was 37/280 (13%). Women in the second group had a 3-fold increased risk to develop GDM (HbA1c 5.7 – 6.4%: 35% vs. HbA1c < 5.7%: 11%, OR 4.1 95% CI 1.4 – 11.8; p = 0.0147). There were no significant differences in mode of delivery, neonatal birthweight, prevalence of macrosomia, or neonatal morbidities.

Conclusion: Pregnant women with a first trimester HbA1c of 5.7 – 6.4% are at higher risk to develop gestational diabetes. Pre-diabetes should therefore be considered as risk factor and prospective studies should focus on question if early intervention versus standard GDM diagnosis criteria is associated with a better short and long term maternal as well as neonatal outcome.