BACKGROUND: Gestational diabetes is associated with adverse maternal and neonatal outcomes with long term implications. Recent studies indicate that these risks are preventable or at least reducible by early detection and appropriate management, therefore screening is ideal. However, it is still controversial to which plasma glucose level of 50g Glucose Challenge Test for screening is best to identify pregnant women at risk for gestational diabetes mellitus. Several studies had shown variations in the cutoff values in different population. In the Philippines, there is no published study with regards to the appropriate cutoff value for screening and for further testing with 3-h 100g Oral Glucose Tolerance Test in the diagnosis of GDM.
OBJECTIVE: To determine the accuracy of the following 50g GCT threshold values: 120mg/dl, 130mg/dl, 140mg/dl, 150mg/dl, 160mg/dl for screening gestational diabetes mellitus using 3-h 100g OGTT as the gold standard.
STUDY DESIGN: Cross-sectional Study (Diagnostic Test)
STUDY SETTING: Tertiary Hospital, Privilege Mothers' Service, Basak, Lapu-lapu City, Cebu
STUDY POPULATION: One thousand four hundred sixty pregnant women under Privilege Mothers' Service were screened from January 2005- December 2009.
METHODOLOGY: A 1-h 50g GCT was performed among all pregnant subjects between 24-28 weeks gestation and followed by a 3-h 100g OGTT within a week to diagnose gestational diabetes mellitus using Carpenter and Coustan diagnostic criteria.
MAIN OUTCOME MEASURES: The sensitivity, specificity, positive, negative predictive values of the various threshold values were computed. The receiver operating characteristic curve (ROC) was used to determine the most accurate cut-off value of 50-g GCT. Results: The prevalence rate of GDM in this study population was 3.1% (44/1406). The sensitivities of the following cut-off values were 120mg/dl, 130mg/dl, 136mg/dl, 140mg/dl, 150mg/dl and 160mg/dl were 73%, 66%, 68%, 50%, 34%, and 25%, respectively. The specificities were 26%, 85%, 81%, 91%, 94%, and 97%, respectively. The positive predictive values were 3%, 12%, 10%, 15%, 17% and 22%, respectively. The negative predictive values were 97%, 99%, 99%, 98%, 97.7%, and 97.5%, respectively. The Receiver Operating Characteristic Curve (ROC) curve identified a GCT threshold value of 136 mg/dl for detecting GDM, which showed the sensitivity of 68% and false positive rate of 19%.
CONCLUSION: The threshold of 136mg/dl maybe recommended as a better cut-off value of 1-h 50g-GCT with higher accuracy for universal screening of gestational diabetes mellitus and for further testing with 3-h 100g OGTT in the diagnosis of GDM.