BACKGROUND/OBJECTIVES: Low early pregnancy serum 25-hydroxy vitamin D (25[OH]D) levels can increase gestational diabetes mellitus (GDM) risk, although inconsistent findings related to that association have been reported. This study examined the association of serum vitamin D with GDM and the possible influencers on this association. SUBJECTS/METHODS: This study included 259 pregnant women within the Seremban Cohort Study (SECOST). Blood samples at < 14 weeks of gestation were drawn to determine serum 25(OH)D levels. GDM diagnosis was made at 24 to 32 weeks of gestation using a standard procedure. Association between serum vitamin D and GDM was tested using binary logistic regression. RESULTS: Nearly all women (90%) had mild (68.3%) or severe (32.2%) vitamin D deficiency (VDD). Non-GDM women with mild VDD had a significantly higher mean vitamin D intake than GDM women with mild VDD (t = 2.04, p < 0.05). Women with higher early pregnancy serum vitamin D levels had a greater risk of GDM. However, this significant association was only identified among those with a family history of type 2 diabetes mellitus (T2DM) and in women with a body mass index indicating overweight or obese status. CONCLUSIONS: The high prevalence of VDD in this sample of pregnant women underscores the need for effective preventive public health strategies. Further investigation of this unexpected association between serum vitamin D level and GDM risk in predominantly VDD pregnant women and the potential effects of adiposity and family history of T2DM on that association is warranted.

Introduction: Vitamin D deficiency (VDD) is associated with adverse health outcomes in pregnancy and newborns. This study aims to determine the Vitamin D status among pregnant Malaysian women and its associations with specific maternal & pregnancy characteristics. Methods: This study utilised cross-sectional data from a prospective cohort study of pregnant women in Seremban district in which 259 pregnant women had available vitamin D data. Blood samples were taken <14th week of gestation. Serum 25-hydroxy Vitamin D [25(OH)D] levels were analysed using chemiluminescent microparticle immunoassay (CMIA) technology on the ARCHITECT iSystem and categorised using the Institute of Medicine (IOM) 2011 cut offs. A set of pre-tested interviewer-administered questionnaire was used to obtain information on socio-demographics, obstetrics, and anthropometry. Results: Mean serum 25(OH)D was 32.83±11.37nmol/L. The prevalence of severe and mild VDD was 23.2% (n=60) and 68.3% (n=177), respectively. About 8.5% (n=22) of pregnant women were vitamin D insufficient and none had sufficient serum 25(OH)D (>75nmol/L). Early pregnancy body mass index (AOR=2.95, 95% CI=1.03-8.47), working status (AOR=3.17, 95% CI=1.06–9.50) and gravidity (AOR=0.68, 95% CI=0.48–0.98) were significantly associated with VDD. Conclusion: The present study showed a high prevalence of VDD among pregnant women in Malaysia, especially among those who were overweight or obese, working in indoor environment and primigravida.