Seasonal Pattern in Gestational Diabetes Mellitus in Poland: A Retrospective Cohort Study

SIMPLE SUMMARY: This article examines pregnancy results in a changed metabolism, with more frequent glucose intolerance and subsequent gestational diabetes. Metabolic disturbances may significantly influence foetal development and neonatal health; therefore, a routine checkup of glucose tolerance is performed. Several factors may influence the prevalence of gestational diabetes, including ambient temperature, light exposure, and vitamin D levels. The published data related to seasonal impact are contradictory. We have retrospectively analysed a large cohort of newborns and their mothers. In total, 30,205 newborns and their epidemiological and clinical characteristics were evaluated. We documented that the prevalence of gestational diabetes in Central Europe varied depending on the season; that is, it appears more frequently during the summer, while its prevalence was lowest during the winter (seasons with higher vs. lower insolation). The seasonal variation in the prevalence of gestational diabetes affects both mothers of babies born at term and prematurely. ABSTRACT: The existing literature does not address the question of the seasonal impact on pregnancy in Central-Eastern Europe; therefore, this study was designed to investigate the seasonal variation in gestational diabetes mellitus (GDM) based on a recent Polish sample. The data of 30,205 newborns from singleton pregnancies and their mothers, including the date and gestational age of birth, neonatal sex and weight, maternal age and parity, mode of delivery, ethnicity, and a detailed list of comorbidities (including GDM), were retrospectively analysed. The prevalence of GDM was significantly (p < 0.0001) lower in spring (14.71%) than in the other seasons (16.78%). A higher incidence of GDM was observed for mothers who underwent an oral glucose tolerance test from June to August compared to those who were tested from December to February (17.34% vs. 14.75%, p < 0.0001). Similarly, there were significant differences between seasons with higher and lower insolation. The regression analysis revealed that seasonal patterns were significantly associated with the prevalence of GDM. In conclusion, this large retrospective cohort study demonstrated seasonal changes in GDM risk. The observed seasonal patterns may equally refer to mothers of babies born at term and prematurely. Further research concerning GDM risk and other seasonal and gender associations is warranted.