Objective: To identify 25 hydroxyvitamin D (25OHD) levels in Thai pregnant women with gestational diabetes and nongestational diabetes.
Material and Method: This prospective study was conducted on 197 pregnant women at Rajavithi Hospital, a tertiary care medical center in Bangkok from October 2010 to July 2011. Plasma 25 hydroxyvitamin D concentration and HbA1c level during the 75 g OGTT in gestational diabetes mellitus (GDM) and non-GDM were evaluated. The recommendations of the International Association of Diabetes and Pregnancy Study Groups (IADPSG) were used for diagnosis of GDM in the present study.
Results: In the selected 197 Thai pregnant women aged from 18 to 49 years, the mean age was 32.1 years, and the mean plasma 25OHD level was 34.3 ng/dl. The percentages of patients classified as having 25OHD deficiency (< 20 ng/dl), 25OHD insufficiency and normal 25OHD were 3.1%, 22.3% and 74.6%, respectively. Among the 197 women, 70 patients (34.8%) had GDM. In the GDM group, 29 patients (41.4%) had abnormal 25OHD level of which 5.7% had 25OHD deficiency and 35.7% had 25OHD insufficiency. Among those with GDM, plasma 25OHD concentration was significantly lower than in the non-GDM subjects (32.3 + 10.3 vs. 35.5 + 6.7 ng/dl, p = 0.001). Fasting blood glucose and HbA1C independently predicted low 25OHD levels in Thai GDM subjects after applying regression model and adjusting for age, BMI, trimester and family history of DM (p = 0.031, p = 0.014 respectively). Higher pre-pregnancy BMI was associated with GDM and lower 25OHD level.
Conclusion: Thai pregnant women with GDM had lower levels of 25OHD compared to those without GDM. Only fasting plasma glucose independently predicted low 25OHD levels in GDM subjects.

Keywords: Gestational diabetes mellitus, 25 Hydroxyvitamin D, Fasting plasma glucose, Hemoglobin A1c