Prevalence of vitamin D deficiency in pregnant women and its association with gestational diabetes mellitus

Several reports have linked vitamin D deficiency with an increased risk of gestational diabetes mellitus (GDM). Both of these conditions are alarmingly common in Saudi Arabia, and pose additional risk of developing future metabolic disease. This study, therefore, investigates the vitamin D status amongst pregnant Saudi women, and the potential influence of vitamin D deficiency on metabolic dysfunction, such as GDM. A total of 578 pregnant women (28.8 ± 5.4 years) were recruited for this study during their first trimester of pregnancy (8-12 weeks) and followed up in their second trimester (24-28 weeks), where data were collected from 297 [51.3% (297/578); 28.9 ± 5.3 years] women. The study collected socio-economic, anthropometric and biochemical data, along with dietary intake, physical activity and sun indices. The findings of this study indicate that during the first trimester 81% of women being vitamin D deficient, dropping to 77% in the second trimester. It was also noted that being younger in age, multiparous, having a lower level of education, being a housewife, and living in West Riyadh were all associated with vitamin D deficiency during the first trimester (p < 0.05), and this further corresponded to reduced sun exposure (p < 0.001). In contrast, physically active pregnant women, women adequately exposed to sunlight at noon (p < 0.001), and residents of North Riyadh all had significantly higher circulating vitamin D levels (p < 0.05). Furthermore, low levels of high-density lipoprotein cholesterol (HDL-cholesterol) during early pregnancy were also associated with an increased risk of vitamin D deficiency (p < 0.05). Ultimately, compared with the first trimester, circulating vitamin D levels were significantly higher in the second trimester, after adjustment (p < 0.001). Among the pregnant women studied here, it was subsequently found that 33% developed GDM in the second trimester. Vitamin D deficiency in early pregnancy was associated with significantly higher risk of GDM, and this risk persisted after adjusting for confounding risk factors with regard to both vitamin D deficiency and GDM [odds ratio (OR) 3.97, confidence interval (CI) 1.12-14.15, p = 0.033]. In addition, significantly higher random blood glucose levels, higher glycated haemoglobin (HbA1c), and low HDL-cholesterol in early pregnancy were observed in the GDM subjects, compared to those without GDM (p < 0.05). Furthermore, vitamin D deficiency in mid-pregnancy increased the risk of metabolic syndrome and low HDL-cholesterol, thus pointing to the role of vitamin D in the probability of developing cardiometabolic disease. In summary, a high prevalence of vitamin D deficiency was observed amongst the subjects in this study, namely pregnant Saudi women. Moreover, hypovitaminosis D in early pregnancy was identified as a significant risk factor for the development of GDM. The present study, therefore, suggests that maintaining optimal levels of vitamin D during pregnancy may be a useful intervention in preventing the development of GDM and metabolic syndrome. Along with vitamin D supplementation, lifestyle modification also appears to be critical for maintaining optimal vitamin D levels during pregnancy, thus avoiding pregnancy-related complications.