Weiler H, Brooks SPJ, Sarafin K, Fisher M, Massarelli I, Luong TM, Johnson M, Morisset AS, Dodds L, Taback S, Helewa M, Von Dadelszen P, Smith G, Lanphear BP, Fraser WD, Arbuckle TE. American Journal of Clinical Nutrition 2021 Jun 3:nqab172. doi: 10.1093/ajcn/nqab172
Background
Reports on the adequacy of vitamin D status of pregnant women are not available in Canada.
Objectives
The objectives of this study were to examine vitamin D status across pregnancy and identify the correlates of vitamin D status of pregnant women in Canada.
Methods
Pregnant women (≥18 years) from 6 provinces (2008–2011) participating in a longitudinal cohort were studied. Sociodemographic data, obstetrical histories, and dietary and supplemental vitamin D intakes were surveyed. Plasma 25-hydroxyvitamin D (25OHD) was measured using an immunoassay standardized to LC-MS/MS from samples collected during the first (n = 1905) and third trimesters (n = 1649) and at delivery (n = 1543). The proportion of women with ≥40 nmol/L of plasma 25OHD (adequate status) was estimated at each time point, and factors related to achieving this cut point were identified using repeated-measures logistic regression. Differences in 25OHD concentrations across trimesters and at delivery were tested a using repeated-measures ANOVA with a post hoc Tukey’s test.
Results
In the first trimester, 93.4% (95% CI: 92.3%–94.5%) of participants had 25OHD ≥40 nmol/L. The mean plasma 25OHD concentration increased from the first to the third trimester and then declined by delivery (69.8 ± 0.5 nmol/L, 78.6 ± 0.7 nmol/L, and 75.7 ± 0.7 nmol/L, respectively; P < 0.0001). A lack of multivitamin use early in pregnancy reduced the odds of achieving 25OHD ≥40 nmol/L (ORadj = 0.33; 95% CI: 0.25–0.42) across all time points. Factors associated with not using a prenatal multivitamin included multiparity (ORadj = 2.08; 95% CI: 1.42–3.02) and a below-median income (ORadj = 1.39; 95% CI: 1.02–1.89).
Conclusions
The results from this cohort demonstrate the importance of early multivitamin supplement use to achieve an adequate vitamin D status in pregnant women.