The diagnostic accuracy of HbA1c in detecting gestational diabetes mellitus among Chinese pregnant individuals.

Background: This study aims to investigate the diagnostic value of the glycated hemoglobin (HbA1c) test for detecting gestational diabetes mellitus (GDM) in pregnant Chinese patients.

Methods: We enrolled a large cohort of 19,261 pregnant individuals who had both oral glucose tolerance test (OGTT) and HbA1c test between 24 and 28 weeks of gestation in a large Chinese tertiary hospital consecutively from 2013 to 2018. We used Pearson's correlation test to evaluate the correlation between OGTT and HbA1c. The diagnostic accuracy of HbA1c for GDM was examined with the receiver operating characteristic curve, using OGTT as the reference standard.

Results: A total of 3,547 (18.42%) women were diagnosed with GDM. HbA1c was positively, but only weakly correlated with the fasting, 1-hour glucose, and 2-hour glucose (r=0.31, 0.24, and 0.25, respectively, all P<0.001). The area under the curve of the HbA1c level for detecting GDM was 0.664 (95% CI: 0.653-0.674, P<0.01). The optimal cut-off point of HbA1c for GDM diagnosis was determined at 5.0% (31 mmol/mol), which yielded a sensitivity of 60.1%, a specificity of 65.3%, a positive predictive value of 28.1%, and a negative predictive value of 87.9%.

Conclusions: HbA1c test is weakly correlated with OGTT during pregnancy, and it offers only limited value in diagnosing GDM among Chinese pregnant individuals.