It is becoming increasingly recognised that vitamin D has roles beyond bone health. Vitamin D deficiency is becoming a major public health problem in Australia. This is attributed to sedentary lifestyle, limited sun exposure, skin pigmentation and religious veiling. Recent studies have shown conflicting evidence on the relationship between vitamin D insufficiency and gestational diabetes mellitus (GDM).
We aimed to study the local incidence of vitamin D deficiency in pregnant women attending the antenatal service at the Canterbury Hospital. Furthermore, we aimed to examine if there is a relationship between vitamin D insufficiency and the development of GDM.
Methods
We performed a prospective, case-controlled study whereby we collected 25-hydroxyvitamin D and calcium levels in pregnant women who presented for publically funded antenatal care at Canterbury Hospital during August 2011 to December 2013. Questionnaires with demographic details were also collected.
Women were eligible if they were over the age of 18yrs and under 46yrs, with a singleton pregnancy, and an initial blood test at ≤ 30 weeks gestation age. Exclusion criteria included pre-existing type I or type II diabetes, inflammatory bowel disease, coeliac disease and those patients who were unable to provide consent due to reduced cognitive ability. GDM was diagnosed as per the Australasian Diabetes in Pregnancy Society criteria (1). Vitamin D insufficiency is defined as 25 hydroxy-vitamin D levels of 49 nmol/L or less.
Results
A total of 785 women enrolled in this study. 40 women were excluded, mostly due to late presentation, incomplete data and lost to follow-up. The incidence of GDM in our population was 23.6%, much higher than the reported NSW average of 7.5% (2). There was no association between vitamin D levels and GDM. The only statistically significant predictors for GDM was complexion. This suggests that ethnicity, not vitamin D status, is the main predictor for GDM.