Predictors of vitamin D status in pregnant women in New Zealand.

Introduction: Newborn vitamin D status is largely determined by maternal vitamin D status during pregnancy. New Zealand has a sun avoidance health policy and minimal dietary vitamin D fortification. Vitamin D deficiency (serum 25-hydroxyvitamin D (25(OH)D) concentration <50 nmol/L) is present in 57% of a sample of newborns from Christchurch and Wellington. To inform vitamin D supplementation policy, our aim was to describe the frequency of, and factors associated with, vitamin D deficiency during pregnancy.

Methods: We enrolled an ethnically diverse sample of pregnant women from a community maternity clinic in South Auckland, New Zealand, with serum 25(OH)D concentration measured at 27 weeks gestation. We examined the associations of enrolment season, maternal demographics, health, sunlight exposure and vitamin D intake with vitamin D deficiency.

Results: Vitamin D deficiency was present in 109/259 (42%). Enrolment season (P<0.001) and ethnicity (P=0.003) were independently associated with the odds of vitamin D deficiency, but not sunlight exposure or dietary vitamin D intake. Of those enrolled in winter (June-August)/spring (September-November), vitamin D deficiency was present in 43% of European, 67% of Māori, 80% of Pacific and 59% of women of other ethnic groups.

Conclusions: These findings suggest that New Zealand's targeted strategy for vitamin D supplementation may miss up to 42% of women with vitamin D deficiency in our population. Supplementation for all pregnant women during winter/spring could be an appropriate intervention for prevention of vitamin D deficiency during pregnancy in New Zealand.