Vitamin D supplementation, cord 25-hydroxyvitamin D and birth weight: Findings from the Odense Child Cohort.

BACKGROUND & AIMS: Hypovitaminosis D, defined as serum 25-hydroxyvitamin D (s-25(OH)D) <50 nmol/L, is frequent in pregnant women and neonates worldwide and has been associated with both low birth weight (BW) and placental weight (PW) as well as reduced placental development. We aimed to assess the prevalence and the risk factors of cord vitamin D deficiency (s-25(OH)D <25 nmol/L) and insufficiency (s-25(OH)D 25-50 nmol/L) and to evaluate the association between cord s-25(OH)D levels and neonatal outcomes (BW, PW and PW/BW ratio).

METHODS: Women enrolled in Odense Child Cohort, a Danish observational prospective population-based cohort, who gave birth to singletons and donated a blood sample for s-25(OH)D measurements were included (n = 2082).

RESULTS: The prevalence of cord vitamin D deficiency was 16.7% and 41.0% for insufficiency. White skin, winter season at birth, maternal supplementation dose of <15 μg/day, non-western ethnicity and high body mass index (BMI) were identified as independent risk factors of both vitamin D deficiency and insufficiency. Adherence to the recommended vitamin D supplementation dose (10 μg/day) was reported by 87% (primipara 91% vs. multipara 81%, p < 0.0001). An U-shaped relationship between cord s-25(OH)D and BW was visualized by spline regression (p = 0.003). After adjustment, cord s-25(OH)D was positively associated with BW (β = 1.522, p = 0.026), PW (β = 0.927, p < 0.001) and PW/BW ratio (β = 0.018, p < 0.001), largely driven by positive associations for cord s-25(OH)D >60 nmol/L.

CONCLUSION: Cord hypovitaminosis D was present in 57.7%. Multipara was identified as a novel risk factor of non-adherence to vitamin D supplementation recommendations; and a maternal supplementation dose <15 μg/day as a novel, independent risk factor of cord hypovitaminosis D. Higher BW, PW, and PW/BW ratio were associated to higher cord s-25(OH)D levels with a suggested cut-off at 60 nmol/L. More studies are encouraged to elucidate the impact of cord s-25(OH)D levels on offspring health and to establish optimal cut-offs for these outcomes.