Seasonal Pattern in the Diagnosis of Gestational Diabetes Mellitus in Southern Sweden

Abstract

Aim. The aim of this study was to examine seasonal patterns in glucose tolerance and in the diagnosis of gestational diabetes mellitus (GDM). Methods. Altogether, 11 538 women underwent a 75-g oral glucose tolerance test (OGTT) in the twenty-eighth week of pregnancy during the years 2003–2005 in southern Sweden. GDM was defined by the 2-h capillary glucose concentration in the OGTT (≥8.9 mmol/L). Chi-squared test, analysis of variance, and regression analyses were used for statistical evaluations. Results. The seasonal frequency of GDM ranged from 3.3% in spring to 5.5% in summer (p < 0.0001). Mean 2-h glucose concentrations followed the same seasonal trend, with a difference of 0.15 mmol/L between winter and summer (p < 0.0001). The 2-h glucose level increased by 0.009 mmol/L for every degree increase in temperature (p < 0.0001). In regression analysis, summer (June–August) was associated with increased 2-h glucose level (p < 0.001) and increased frequency of GDM compared to the other seasons (odds ratio 1.51, 95% confidence interval 1.24–1.83, and p < 0.001). Conclusions. Our findings suggest seasonal variation in the 2-h glucose concentration in the OGTT and in the proportion of women diagnosed with GDM, with a peak in the summer.

Seasonal variations in incidence and maternal–fetal outcomes of gestational diabetes

“…Our finding that glucose levels in pregnancy varied with ambient temperature is in keeping with a number of previous studies [7,8,10,12,14,15] from various settings around the world. At hotter temperatures, the impact of a fixed glucose load may be greater due to reduced circulating plasma volume, leading to increased diagnoses of GDM.…”

“…In addition to risk associated with individuals, however, there may also be factors in the general environment that influence the likelihood of GDM. Several recent reports suggest that GDM incidence varies with season in diverse settings including southern Europe [7][8][9], Brazil [10], Australia [11][12][13] and Canada [14,15]. These studies show that postload glucose values and incidence of GDM increase at higher ambient temperatures [7,8,10,13,14].…”

“…In the present study, we aimed to explore the association between time of year and GDM diagnosis in a cooler climate with less annual variation than many settings previously studied [7,11,13,14]. In Cambridge, UK, the average annual daily temperature is 11.2°C, with average monthly maximum temperatures between 7.3°C (January) and 22.8°C (July) [16].…”

Temporal Trends without Seasonal Effects on Gestational Diabetes Incidence Relate to Reductions in Indices of Insulin Secretion: The Cambridge Baby Growth Study

“…This is despite seasonal trends in GDM previously have been observed in populations in Sweden 13 , Australia 14, 15 , Italy 16 and Greece 17 . However of the populations tested before where no such trend was observed 18,19 one of these was also in the U.K. 19 so our lack of seasonal trend may relate to climate or other environmental factors specific to the U.K. Alternatively, whilst at least one of the studies that found a seasonal trend used a very similar analysis technique to the one that we used 15 , other studies used analysis of variance or categorical/ordinal analyses which did not account for the recurring nature of the seasons or adjust for longer-term temporal trends 13,14,16,17 so differences from our results may relate to this.…”

“…9 Therefore another factor that could explain at least part of the increased incidence of GDM is exposure to raised or rising ambient temperatures in certain populations. [10][11][12] Following this some studies have reported seasonal variations in the incidence of GDM [13][14][15][16][17] , although this has not been observed in all populations or climates. 18,19 In this study we investigated whether there were temporal and seasonal trends in GDM incidence in our single centre population from Cambridge, U.K. which recruited pregnant women between 2001 and 2009.…”