Pregnant women may be sweeter in the summer: Seasonal changes in glucose challenge tests results. A population-based study

Aims: A 1-hour, 50-gram glucose challenge test (GCT) is the first step in the diagnosis of gestational diabetes mellitus (GDM). Seasonal fluctuations in fasting glucose levels and GCT results were previously described. We sought to investigate seasonal changes in GCT results in a large cohort. Methods: GCT results were analyzed of all women insured at the Central District of Clalit Health Services (the largest health maintenance organization in Israel), between the years 2005 and 2016. Results: A total of 101,359 GCT results were analyzed. Mean GCT was 110 ± 28.9 mg/dL, and 14.5% (n = 14,652) were pathological. Both the mean and the incidence of pathological GCT were lowest in the winter, followed by spring, fall, and summer, (p for trend < 0.001). The difference in mean GCT between winter and summer was 7.82 ± 0.24 mg/dL (95% CI, 7.35–8.29). After adjustment for BMI and age, having a GCT in the winter was independently associated with the lowest risk for pathological GCT, as compared to all other seasons. Conclusions: Seasonal changes in GCT results should be studied further in additional regions, and if found, the cutoff threshold for abnormal GCT should be re-examined and adapted to local weather conditions and seasonal variability.