Post-Hoc Analysis of Vitamin D Status and Reduced Risk of Preterm Birth in Two Vitamin D Pregnancy Cohorts Compared With South Carolina March of Dimes 2011 Rates

Carol L. Wagner, Carole A. Baggerly, Sharon L. McDonnell, Keith A. Baggerly, Christine B. French, Leo L. Baggerly, Stuart A. Hamilton, Bruce W. Hollis

Women with serum 25(OH)D concentrations ≥40 ng/mL (n = 233) had a 57% lower risk of preterm birth compared to those with concentrations <20 ng/mL [n = 82; RR = 0.43, 95% confidence interval (CI) = 0.22,0.83]; this lower risk was essentially unchanged after adjusting for covariates (RR = 0.41, 95% CI = 0.20,0.86). The fitted LOESS curve shows gestation week at birth initially rising steadily with increasing 25(OH)D and then plateauing at ≥40 ng/mL. Broken down by race/ethnicity, there was a 79% lower risk of preterm birth among Hispanic women with 25(OH)D concentrations ≥40 ng/mL (n = 92) compared to those with 25(OH)D concentrations <20 ng/mL (n = 29; RR = 0.21, 95% CI = 0.06,0.69) and a 45% lower risk among Black women (n = 52 and n = 50; RR = 0.55, 95% CI = 0.17,1.76). There were too few white women with low 25(OH)D concentrations for assessment (n = 3). Differences by race/ethnicity were not statistically significant with 25(OH)D included as a covariate.

Compared to the CC-MOD reference group, women with serum concentrations ≥40 ng/mL in the combined cohort had a 46% lower rate of preterm birth overall (n = 233, p = 0.004) with a 66% lower rate among Hispanic women (n = 92, p = 0.01) and a 58% lower rate among black women (n = 52, p = 0.04).

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