Vitamin D levels in an Australian and New Zealand cohort and the association with pregnancy outcome

Background: Pregnant women are at increased susceptibility to vitamin D deficiency. Hence, there is continuing interest in determining how vitamin D influences pregnancy health. We aimed to compare vitamin D status in two distinct populations of pregnant women in Australia and New Zealand and to investigate the relationship between vitamin D status and pregnancy outcome. This included evaluating possible effect measure modifications according to fetal sex. Methods: Serum 25-hydroxy vitamin D (25(OH) D) was measured at 15 +/- 1 weeks' gestation in 2800 women from Adelaide and Auckland who participated in the multi-centre, prospective cohort SCreening fOr Pregnancy Endpoints (SCOPE) study. Results: Mean serum 25(OH) D in all women was 68.1 +/- 27.1 nmol/L and 28% (n = 772) were considered vitamin D deficient ( 81 nmol/L) "standardised" vitamin D status when compared to moderate-high (63-81 nmol/L, aRR, 0.47; 95% CI: 0.23, 0.96). Marginal sex-specific differences occurred between vitamin D status and GDM: women carrying a female fetus had a 56% decreased risk for GDM in those with low-moderate levels of standardised vitamin D (44-63 nmol/L) compared to moderate-high levels (aRR: 0.44; 95% CI: 0.20, 0.97), whilst in women carrying a male fetus, a 55% decreased risk of GDM was found with high standardised vitamin D when compared to moderately-high vitamin D, but this was not statistically significant (aRR: 0.45; 95% CI: 0.15, 1.38). Conclusions: High serum 25(OH) D at 15 +/- 1 weeks' gestation was shown to be protective against the development of GDM. A possible association between fetal sex, vitamin D status and GDM provides further questions and encourages continual research and discussion into the role of vitamin D in pregnancy, particularly in vitamin D replete populations