Effectiveness of Glycated Haemoglobin in the Diagnosis of Gestational Diabetes Mellitus Among Pregnant Women in Port Harcourt, Nigeria

Background: Gestational Diabetes Mellitus (GDM) is a common metabolic complication in pregnancy with a broad range of adverse foetal and maternal outcomes if not properly managed. Due to the difficult nature of the Oral glucose tolerance test (OGTT), the utilization of the Glycatedhaemoglobin (HbA1c) test as a simpler and acceptable alternative has been suggested. The aims were to determine the GDM prevalence, the diagnostic accuracy, the optimal cut-off point and the validity of the HbA1c in diagnosing GDM using OGTT as the gold standard in the University of Port Harcourt Teaching Hospital (UPTH).

Methodology: This was a prospective cross-sectional study involving a cohort of 250 antenatal attendees at 24-28 weeks of pregnancy in the UPTH from 1st February 2018 - 30th April 2018. Socio-demographic data and results of the OGTT and HbA1c tests were analysed using SPSS 21.0 for windows® statistical software. The area under the Receiver Operating Characteristics (ROC) curve was used to determine the diagnostic accuracy of HbA1c. The Youden index was used to get the optimal cut-off point for HbA1c. The validity of the HbA1c was determined using sensitivity, specificity, positive predictive value and negative predictive value. The P-value at p<0.05 was set as the level of significance.

Results: Out of the 250 women, 36 (14.4%) had GDM hence in this study, the GDM prevalence was 14.4%. Area under the curve (AUC) = 0.649; 95% confidence interval: 0.550 - 0.748; p-value = 0.004. The optimal cut-off point for HbA1c was 5.18% with a sensitivity of 63.9%, a specificity of 59.3%, a positive predictive value of 20.9% and a negative predictive value of 90.7%.

Conclusion: The HbA1c at the Optimal cut-off point of 5.18% in our environment cannot replace the OGTT in the diagnosis of GDM because of its low sensitivity and specificity but will be useful in the screening for GDM because of its high negative predictive value at 24-28 weeks gestation. This will reduce the count of gravidae who undergo the cumbersome OGTT.