To determine the effect of different seasons on the prevalence of gestational
diabetes mellitus (GDM) by using World Health Organization criteria.
RESEARCH DESIGN AND METHODS
The results of all pregnancy glucose tolerance tests (GTTs) were prospectively
collected over a 3-year period in a temperate climate, and the results were
grouped by season.
The results of 7,369 pregnancy GTTs were available for consideration. In winter, the
median 1-h and 2-h glucose results after GTT were significantly (P < 0.0001) lower
than the overall 1-h and 2-h results. The prevalence ofGDMat the 1-h diagnostic level
was 29% higher in summer and 27% lower in winter than the overall prevalence (P =
0.02). The prevalence of GDM at the 2-h diagnostic level was 28% higher in summer
and 31% lower in winter than the overall prevalence (P = 0.01).
The prevalence of GDM varies according to seasons, which leads to the possible
overdiagnosis of GDM in summer and/or underdiagnosis in winter. Further research
into standardization of the GTT or seasonal adjustment of the resultsmay need to be