Vitamin D status and its predictive factors in pregnancy in 2 Australian populations

High prevalence rates of suboptimal vitamin D levels have been observed in women who are not considered ‘at risk’. The effect of behavioural factors such as sun exposure, attire, sunscreen use and vitamin D supplementation on vitamin D levels in pregnancy is unknown. The aim of this study was to determine prevalence and predictive factors of suboptimal vitamin D levels in 2 antenatal clinics in Australia - Campbelltown, NSW and Canberra, ACT. A cross-sectional study of pregnant women was performed with a survey of demographic and behavioural factors and a mid-pregnancy determination of maternal vitamin D levels. The prevalence of vitamin D deficiency (≤25 nmol/L) and insufficiency (26-50 nmol/L) was 35% in Canberra (n = 100) and 25.7% in Campbelltown (n = 101). The majority of participants with suboptimal D levels had vitamin D insufficiency. Among the vitamin D-deficient women, 38% were Caucasian. Skin exposure was the main behavioural determinant of vitamin D level in pregnancy in univariate analysis. Using pooled data ethnicity, season, BMI and use of vitamin D supplements were the main predictive factors of suboptimal vitamin D. Vitamin D supplementation at 500 IU/day was inadequate to prevent insufficiency. Behavioural factors were not as predictive as ethnicity, season and BMI. As most participants had one of the predictive risk factors for suboptimal vitamin D, a case could be made for universal supplementation with a higher dose of vitamin D in pregnancy and continued targeted screening of the women at highest risk of vitamin D deficiency.