Does the gestational age at which the glucose challenge test (GCT) is conducted influence the diagnosis of gestational diabetes mellitus (GDM)?

Purpose: This study’s objective is to investigate disparities in the rates of gestational diabetes mellitus (GDM) diagnosis, influenced by the timing of the glucose challenge test GCT. Methods: This retrospective cohort study included women with singleton or twin pregnancies exhibiting abnormal GCT result between 24 and 28 weeks of gestation, followed by an oral glucose tolerance test OGTT during the same period. Data regarding pregnancy follow-up from patients’ deliveries at a singular tertiary medical from 2014 to 2022 were retrieved. The probability of GDM diagnosis was stratified based on the gestational week of the GCT and the definition of a positive OGTT, delineated by one or two abnormal values. Results: The study included 636 women with abnormal GCT between 24 and 28 weeks of gestation. Of them, 157 unerwent the GCT between 24.0 and 24.6 weeks, 204 between 25.0 and 25.6 weeks, 147 between 26.0 and 26.6 weeks, and 128 between 27.0 and 28.6 weeks. We found that the highest incidence of GDM, defined by one or two pathological values of the OGTT, following the initial screening with a GCT, where abnormal results were defined as values exceeding 140 mg/dL, was diagnosed in patients who underwent GCT between 26.0 and 26.6 weeks of gestation. Conversely, the lowest rates were observed in patients screened between 24.0 and 24.6 weeks of gestation. Conclusion: The timing of screening for GDM using the GCT significantly affects the rate of diagnosis. Clinicians managing pregnancies should consider this data when formulating treatment plans.