Is There a Seasonal Variation in the Incidence of Gestational Diabetes?

Abstract

It has been suggested that the incidence of gestational diabetes (GDM) may vary with different seasons of the year. The fasting and 2 h glucose levels after a 75 g glucose tolerance test were therefore examined in 2749 women being tested for GDM and were correlated with the mean temperature at 0900 h by month and by season. The mean monthly temperature ranged from 22.3 degrees C in January to 13.6 degrees C in July. The monthly incidence of GDM ranged from 3.5% (95% CI, 0.7-6.3) in September to 8.7% (4.7-12.7) in November. The seasonal incidence of GDM ranged from 7.4% (5.6-9.2) in autumn to 5.5% (3.5-7.5) in winter. Chi-squared analysis did not suggest a significant association between the proportion of women diagnosed with GDM and either the month (p = 0.47) or the season (p = 0.39). Multiple regression analysis, after correction for maternal age, parity, BMI, and the week of testing revealed a non-significant association between fasting glucose and monthly temperature (p = 0.36) and an increase in the 2 h glucose of 0.026 mmol l-1 for each increase of 1 degree C in temperature (p = 0.011). In a temperate coastal area of Australia these differences do not appear clinically significant and have not caused a variation in the incidence of GDM with different seasons.