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

Background: 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. Aim: To determine prevalence and predictive factors of suboptimal vitamin D levels in 2 antenatal clinics in Australia - Campbelltown, NSW and Canberra, ACT. Methods: 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. Results: 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. Conclusions: 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.