Winter conception increases gestational diabetes risk

A study led by the University of Adelaide has found that women whose babies are conceived in winter are more likely to develop gestational diabetes — a serious pregnancy complication characterised by inadequate blood sugar control. Complications of gestational diabetes include excessive birth weight, preterm birth, low blood sugar and the development of type 2 diabetes later in life.

In the first population-based study of its kind, the university’s Robinson Research Institute investigated more than 60,000 births in South Australia over a five-year period. The researchers collaborated with the University of Groningen in the Netherlands and the Pregnancy Outcome Unit of SA Health on the study, with the results published in the journal BMJ Diabetes Research & Care.

The team found that in the five years from 2007–2011, the incidence of pregnancies affected by gestational diabetes increased from 4.9% in 2007 to 7.2% in 2011. Women who conceived in winter were more likely to develop gestational diabetes during their pregnancy, with 6.6% of pregnancies from winter conceptions affected, and were additionally at high risk of developing type 2 diabetes within the five years after delivery as well as cardiovascular disease. Women who conceived in summer were meanwhile less likely to develop gestational diabetes, with 5.4% of summer conceptions affected.

“Our study is the first of its kind to find strong evidence of a relationship between gestational diabetes and the season in which a child is conceived,” said lead author Dr Petra Verburg from the University of Groningen, currently based at the Robinson Research Institute, who noted that the mechanisms that cause gestational diabetes are still not fully understood.

“Previous studies have suggested that meteorological factors, physical activity, diet and vitamin D are risk factors for gestational diabetes, all of which are impacted by the winter season,” she said.

Fitted seasonality for gestational diabetes mellitus (GDM) by estimated date of conception (eDoC). The histogram represents the observed probability of GDM by eDoC (divided in calendar months). The dashed line represents the unadjusted Fourier fit for the incidence of GDM by eDoC. The bold line represents the adjusted Fourier fit for the incidence of GDM by eDoC. The adjusted Fourier fit was adjusted for maternal age, BMI, parity, ethnicity, socioeconomic status and chronic hypertension. Image courtesy of the authors under CC BY-NC 4.0

Senior author Professor Claire Roberts believes vitamin D deficiency is a likely candidate, citing “a number of studies in different countries that have shown that women with low vitamin D are more likely to develop gestational diabetes”.

“Obviously in winter we have lower exposure to ultraviolet light, so the work we are doing is looking at investigating vitamin D as being a seasonal factor and how that contributes to pregnancy complications,” said Professor Roberts, who is based at the Robinson Research Institute. She said the data showed a strong correlation between vitamin D and elevated BMI as well.

“Elevated BMI and low physical activity are risk factors for gestational diabetes, as well as low socioeconomic status,” Professor Roberts said. “These factors are modifiable, and they represent targets for interventions to prevent the rising tide of gestational diabetes.

“Women need to look after themselves better than they do now with better diets, and maybe losing weight before conception, to give themselves the best possible chance,” she said.

Top image courtesy of erik langner under CC BY-SA 2.0