Background: Gestational diabetes mellitus (GDM) has serious consequences such as increased risks of preeclampsia, macrosomia and cesarean delivery. Even though the mechanistic basis of GDM has not been completely understood, several risk factors have been identified and one of these is vitamin D. However, the link between vitamin D deficiency and development of GDM is yet to be proven with certainty.
Methods: This study aimed to investigate the link between the incidence of GDM and serum vitamin D level in pregnant women of Saudi Arabia. 515 Saudi women (ages 18-46) in their 24-28th week of pregnancy, visiting various hospitals of Riyadh, participated in this study. Serum vitamin D and various biochemical and anthropometric parameters were determined in the first trimester and the recruits were screened for GDM by OGTT according to IADPSG criteria in their 2nd trimester. The association between vitamin D deficiency and development of GDM was calculated based on odds ratio of the incidence of GDM among vitamin D deficient and normal women.
Results: In this study cohort of 515 pregnant women, in the first trimester vitamin D deficiency (< 50 nmol/l) was detected in 425 (82.5%). On their 2nd visit (2nd trimester), 116 (27.7%) were diagnosed with GDM out of 419 with OGTT, according to IADPSG criteria. GDM risk was significantly higher among vitamin D deficient than non-deficient women (Odds Ratio: 2.87; Confidence Interval: 1.32-6.25; P = 0.008) even after adjusting for season, sun exposure and vitamin D intake (OR: 2.9; CI: 1.07-7.89). Of the various anthropometric and biochemical parameters, the GDM women differed significantly from non-GDM women with respect to serum levels of triglycerides (in mmol/l) (1.3 ± 0.6; 1.5 ± 0.6, p = 0.018) and fasting glucose (in mmol/l) [4.7 (4.3-5.2); 5.1 (4.6-5.6), p < 0.01]. Also, fasting glucose level in the 2nd trimester correlated inversely to serum vitamin D level determined during the 1st trimester (r = - 0.121; p = 0.014).
Conclusions: Results of our study reveal a significantly higher risk of development of GDM among pregnant women having deficient vitamin D status.
Keywords: 25(OH) D; Gestational diabetes mellitus; Insulin resistance; Oral glucose tolerance test; Type 2 diabetes mellitus.