Reproducibility Assessment of the One-step 75 g Oral Glucose Tolerance Test for Diagnosing Gestational Diabetes Mellitus

Objective: To assess the reproducibility of the one-step 75-g oral glucose tolerance test (OGTT) for diagnosing gestational diabetes mellitus (GDM). Methods: We included a consecutive sample of adult pregnant women before 24 gestational weeks from the antenatal care clinic. Demographic and clinical characteristics were obtained and a75-g OGTT was performed at 24, 26, and 28 weeks of gestation following standardized international recommendations. We determined reproducibility and diagnostic accuracy measures. Results: We included ninety-two pregnant women (mean age 26.27 ± 6.51 years). A total of 69 (75%) patients had a normal OGTT in the three consecutive tests. Twenty-three patients (25%) were diagnosed with GDM with one altered OGTT, and only 7 (30.4%) and 2 (8.6%) maintained the diagnosis in two or three OGTTs. Screening with one 75-g OGTT exhibited low sensitivity (39.1-52.1%), which increased when two OGTTs (83.1-86.2%) were used compared to the results obtained with three OGTTs. Standard deviations and reproducibility limits were greater in the GDM group. Conclusions: The one-step 75-g OGTT has a limited reproducibility, which could lead to potential GDM over- and underdiagnosis. Further studies that evaluate the impact of diagnosing GDM and neonatal and maternal outcomes with one versus a second or third 75-g OGTT are needed.