EVALUATION OF ORAL GLUCOSE TOLERANCE TEST, HAEMOGLOBIN A1C AND INSULIN RESISTANCE IN DIAGNOSIS OF GESTATIONAL DIABETES MELLITUS
Abstract
Background: The diagnosis of Gestational Diabetes Mellitus (GDM), a disease
characterised by increased insulin resistance is particularly challenging in view of plethora of diagnostic criteria. The need to prevent adverse pregnancy outcome and recent standardization and use of glycated haemoglobin (HbA1C) in diagnosis of Diabetes Mellitus has respectively given birth to a downward review in the ADA criteria and a call for use of HbA1C in diagnosis of GDM.
Objective: The main objective of this study was to evaluate HbA1C, Insulin Resistance
index and the recent ADA diagnostic criteria in comparison with the established WHO criteria in the diagnosis of GDM
Method: This was a cross-sectional study involving one hundred and fifty pregnant
women at estimated 24-32 weeks of gestation of pregnancy. During a standard Oral Glucose Tolerance Test (OGTT), blood samples were collected for measurement of HbA1C, fasting, 1hour and 2-hour glucose as well as fasting and 2-hour Insulin. The women were classified as Gestational Diabetic (GD) and non Gestational Diabetic (NGD) based on the ADA and WHO diagnostic criteria. The Insulin sensitivity index (Matsuda Index) was computed and a cut-off of ≤ 4.1 was used to identify women with significant insulin resistance. Clinical and biochemical characteristics were compared among the groups using Student’s t-test with significance level set at P< 0.05. Receiver Operative Characteristic (ROC) curve was used to assess the predictive ability of HbA1C and Matsuda Index for GDM.
Results: A total of 35 women were diagnosed as GDM, 30 women by ADA criteria and
20 women by WHO criteria. Forty-two (28%) of the women had significant insulin resistance. Glucose, Insulin and HbA1C were significantly higher in the GD than NGD groups (P<0.01). The Odd Ratio of the ADA and WHO diagnostic criteria for identifying insulin resistance was 3.4 (1.5-7.9) 95%CI and 8.5 (3.0-24.1) 95%CI respectively. Ninety-five per cent of all the subjects with GDM had Matsuda Index ≤ 7.5 and only 3% of non GDM subject
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(by either ADA or WHO criteria had a Matsuda score of ≤ 2.4. At a cut-off of ≥ 6.0%, HbA1C predicted GDM with 95% specificity and sensitivity of 27% and 35% for ADA and WHO criteria respectively.
Conclusion/Recommendation: WHO diagnostic criteria showed better
correlation and association with biochemical indices of GDM than the ADA criteria. HbA1C may not be an effective individual diagnostic test for GDM in many patients; however, its utility may be enhanced by combining it with OGTT. A Matsuda Index of ≤ 2.4 suggests severe insulin resistance in pregnancy while 2.5-7.5 suggest moderate insulin resistance with potential of progression to GDM. Early measuring of Insulin sensitivity should be done in atrisk pregnancy to identify women at risk of progressing to GDM.
