Determinants of maternal vitamin D concentrations in Slovenia : A prospective observational study

To analyze the vitamin D status of pregnant women in Slovenia and the factors influencing it.

The study was performed in Maribor University Medical Centre (location 46°N). Maternal serum 25-hydroxy-vitamin D (25(OH)D) in 4 groups of 100 pregnant women in 4 different seasons of the year was measured at the time of delivery. Data on life style, eating habits, sunbathing and intake of vitamin D supplements during pregnancy were obtained using a questionnaire. Information on maternal outcome was acquired from medical records. Duration of sunlight and average temperature in the month preceding delivery were calculated from meteorological data.

The average maternal 25(OH)D concentration ranged from 28.5 ± 17.1 nmol/l in March to 54.8 ± 24.1 nmol/l in June (p < 0.001). Severe vitamin D deficiency, i.e. <25 nmol/l 25(OH)D was present in 23.6% of women overall. In multiple regression analysis supplements containing vitamin D (β = 0.225, p < 0.001) and duration of intentional exposure to sunlight (β = 0.192, p = 0.026) were associated with maternal 25(OH)D status. Significantly lower vitamin D levels were observed in women who had a cesarean section (t = 2.053, p = 0.041) and those with premature delivery (t = 2.296, p = 0.022). Vitamin D levels were not associated with the occurrence of gestational diabetes, gestational hypertension or infections during pregnancy.

A high prevalence of vitamin D deficiency was detected at the end of pregnancy, especially in the months following autumn and winter and in women who did not take supplements containing vitamin D.