Gestational diabetes varies with the seasons

Gestational diabetes is defined as elevated blood sugar during pregnancy in women without previous diabetes

Risk factors for gestational diabetes include maternal obesity, increasing maternal age, a family history of type 2 diabetes and previous pregnancy with gestational diabetes.

Studies also suggest that gestational diabetes may be affected by a variety of environmental influences, including ambient temperatures, physical activity in early pregnancy, variations in nutrient intake, and serum vitamin D levels.

It is thought that the aetiology of gestational diabetes involves exposures prior to pregnancy and during early pregnancy — before the condition is diagnosed clinically.

Because of the potential seasonal influences on gestational diabetes and because of the importance of exposures early in pregnancy, researchers in Southern Australia sought to explore the relationship between estimated date of conception and incidence of gestational diabetes.

The study, published by Verburg, et al. in 2016, was a retrospective cohort study.

Data from 60,306 women who gave birth between 2007 and 2011 were sourced from the South Australian Perinatal Statistics Collection.

A total of 3632 cases of gestational diabetes were reported, representing 6% of pregnancies.

After adjusting for confounding variables, seasonal modeling demonstrated statistically significant seasonal variation in gestational diabetes (p<0.001), with peak incidence occurring in pregnancies with winter estimated dates of conception (June, July, August in Australia) and lowest incidence occurring in pregnancies with summer estimated dates of conception (December, January, February in Australia).

Results of this study are consistent with results of the only other study to report seasonal variation in gestational diabetes.

That study, also conducted in Australia, found peak diagnosis of gestational diabetes during the summer, which would correspond to conception dates in the winter.

The retrospective nature of this study did not allow researchers to explore the mechanisms to explain underlying the results.

Ambient temperature, physical activity, nutrient intake or vitamin D status all change with the seasons and may explain why more women develop gestational diabetes when they conceive in the winter.