Aims: The incidence of gestational diabetes has been reported to have risen over the first decade of this century. Some studies have also found it to vary with seasons of the year. We therefore investigated temporal and seasonal trends on gestational diabetes incidence in a single centre cohort study from Cambridge, U.K., and attempted to explain trends using associations with risk factors. Materials and Methods: Using a cosinor model we tested whether there were both temporal and seasonal trends in gestational diabetes incidence in 1,074 women recruited to the Cambridge Baby Growth Study in 2001-2009 who underwent oral glucose tolerance tests around week 28 of pregnancy. We also undertook risk factor analyses. Results: There was a temporal increase in gestational diabetes incidence over the course of recruitment to this study (p=2.1x10-3) but no seasonal effect (p=0.7). HOMA B (p=3.0x10-3; n=1,049) and the insulin disposition index (p=3.0x10-3; n=1,000) showed negative temporal trends. There was no negative association with HOMA S. Risk factor analyses showed a concomitant temporal slight increase in the index of multiple deprivation (p=4.6x10-10, n=1,068). This index was positively associated with HOMA B (p=6.1x10-5, n=955) but not directly with gestational diabetes (p=0.6, n=1,032), HOMA S (p=0.2, n=955) or the insulin disposition index (p=0.4, n=955). Conclusions: In this population there were temporal but not seasonal increases in gestational diabetes incidence between the years 2001 and 2009, which appeared to be related more to reductions in insulin secretion than sensitivity. Possible mediators of this link include confounding factors related to deprivation.

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