Use of Fasting Plasma Glucose and Haemoglobin A1c in Screening for Gestational Diabetes Mellitus in High-risk Antenatal Patients in Hong Kong

Abstract

Objectives: Gestational diabetes mellitus (GDM) is one of the most common medical conditions complicating pregnancy associated with adverse obstetric and perinatal outcomes. There is no worldwide consensus for the ideal screening test and diagnostic criteria for GDM. This study aimed to assess the usefulness of fasting plasma glucose (FPG) and glycated haemoglobin (HbA1c) in screening of the high-risk antenatal population for GDM in a Chinese population.
Methods: This was a 6-month retrospective study of high-risk pregnant women who undertook oral glucose tolerance test (OGTT) and HbA1c test in a tertiary centre in Hong Kong. The World Health Organization (WHO) / National Institute for Health and Care Excellence (NICE) 2008 GDM criteria were used as the gold standard for comparing diagnostic accuracies of fasting glucose and HbA1c.
Results: Of 1328 women qualified for the study, 284 (21.4%) were diagnosed to have GDM according to the
WHO / NICE 2008 criteria. There was significant association between the diagnosis of GDM and the patient age at delivery, maternal obesity, history of impaired glucose tolerance / GDM, and glycosuria. Using the receiver operating characteristic curve and Youden Index, the cut-off level for HbA1c and FPG for the diagnosis of GDM was 5.3% and 4.3 mmol/L, respectively. The screening test was positive when either value met the specified cut-off level. In both groups of all lengths of gestation and 24-30 weeks of gestation, the sensitivity of the test was approximately 90%, specificity and positive predictive values were low, and negative predictive value was similar with gestation-specific calculation (90.7% vs. 93.0%).
Conclusion: Using combined fasting plasma glucose and HbA1c as a first-step screening, OGTT may be avoided in 24.4-27.7% of the patients. Therefore, a combined HbA1c / FPG test may be considered the first-step screening test for GDM. Further studies are required to extend screening to the low-risk population or for establishing the ideal diagnostic criteria for GDM in Hong Kong.