The relationship between markedly elevated glucose challenge test results and the rate of gestational diabetes mellitus and gestational impaired glucose tolerance

Abstract

BACKGROUND AND OBJECTIVES: Even though the 50 g oral glucose challenge test (GCT) is the most commonly used screening modality for gestational diabetes mellitus (GDM), no consensus for the diagnostic approach is available to patients with a markedly elevated GCT result. We aimed to evaluate the diagnostic utility of markedly elevated GCT results and the impact of age using the oral glucose tolerance test (OGTT) as gold standard. DESIGN AND SETTING: Retrospective study conducted in a women's hospital in Ankara, among patients who underwent GCT from January 2005 to December 2008. PATIENTS AND METHODS: In this retrospective study, we included 626 pregnant women who underwent a 3-hour 100 g OGTT after a GCT result ≥180 mg/dL among 29842 women. We calculated positive predictive values (PPV) of each GCT category to diagnose GDM and both GDM and gestational impaired glucose tolerance (GIGT). RESULTS: A GCT result of ≥240 mg/dL provided 100% PPV for the diagnosis of GDM and a result of >230 mg/dL provided 100% PPV for the diagnosis of GDM + gestational impaired glucose tolerance (GIGT), according to both, National Diabetes Data Group (NDDG) and Carpenter and Coustan (CC) criteria. A result of ≥200 mg/dL provided 100% PPV for diagnosing GDM+GIGT in patients older than 35 years, according to the CC criteria. CONCLUSIONS: The GCT result of 200 mg/dL is an ideal cutoff value for the diagnosis of GDM + GIGT in patients ≥35years, and OGTT can be omitted in these patients. In younger patients, the cutoff value should be chosen as 230 mg/dL.