Predicting gestational diabetes mellitus by first trimester HbA1c: a retrospective study in women with moderate to severe obesity

This study aimed to investigate the utility of first trimester HbA1c in predicting gestational diabetes mellitus (GDM) in obese women with Grade II-III obesity. HbA1c was measured during the first trimester in 160 obese women. A 75g oral glucose tolerance test (OGTT) was performed between 24-28 weeks gestation and GDM diagnosed by WHO criteria. The prevalence of GDM was 24%. An HbA1c of <= 28mmol/mol had 100% negative predictive value for GDM. An HbA1c of >= 33mmol/mol had a 69.2% sensitivity and 63.6% specificity for GDM. At higher HbA1c cut-offs, the odds ratio (OR) for developing GDM increased; at a threshold of >= 39mmol/mol, the OR for GDM was 10.1 (95% CI 2.5-40.5). Women with a first trimester HbA1c of >= 28mmol/mol are at very low risk of developing GDM and may not require an OGTT at 28 weeks, while those with HbA1c >= 39mmol/mol may benefit from early glucose monitoring in pregnancy. Copyright (c) 2023 John Wiley & Sons.