Comparative Evaluation of Fasting Plasma Glucose and One Hour ۵۰-G Glucose Challenge Test in Screening Gestational Diabetes Mellitus

Background and Objective: Gestational diabetes is one of the most common metabolic disorders during pregnancy. In order to find out a simple and cost effective method with acceptable sensitivity and specificity, fasting plasma glucose (FPG) and one hour ۵۰-g glucose challenge test (OGCT) were compared in patients with gestational diabetes mellitus (GDM). Materials and Methods: In this prospective cohort study, pregnant women without preexisting diabetes underwent FPG and OGCT tests between ۲۴ and ۲۸ weeks of gestation. If the OGCT threshold values exceeded ≥ ۱۳۰ mg/dl, the ۱۰۰g oral glucose tolerance test (OGTT) was performed using Carpenter and Coustan criteria. Receiver operating characteristic (ROC) analysis was used to evaluate the performance of the two tests. Results: GDM was diagnosed in ۷.۳% and impaired glucose tolerance in ۳.۲%. The best cut-off points for GCT and FPG were ۱۳۴mg/dl(sensitivity: ۹۹.۲۴%, specificity: ۷۶.۵۷%) and ۸۷mg/dl(sensitivity: ۸۰.۱۵%, specificity: ۸۵.۶۲%).By using GCT, an optimal cut-off values of GCT<۱۳۵mg/dl (sensitivity: ۹۶.۹۵%) to rule out GDM and values ≥ ۱۶۵mg/dl (specifity: ۹۶.۱۰%) to rule in GDM, would eliminate the need for the OGTT in ۸۰.۱% women (misclassification rate: ۳.۸۳%). By using FPG, an optimal cut-off values of <۷۶mg/dl (sensitivity: ۹۵.۴۲%) to rule out GDM and values ≥ ۹۱mg/dl (specifity: ۹۵.۵۶%) to rule in GDM, would eliminate the need for the OGTT in ۵۱% women (misclassification rate: ۴.۴۳%). Conclusion: The results showed that the best test for predicting macrosomia, preterm delivery and caesarian section is OGCT and for preeclampsia and respiratory distress is FPG. As OGCT can decrease the necessity of OGTT performance with lower misclassification rate comparing to FPG, OGCT would be the best screening test for GDM in Iran.

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Key words: Fasting plasma glucose ، Gestational diabetes mellitus ، Glucose challenge test ، Glucose tolerance test ، Screening