title: Post-hoc comparison of vitamin D status at three timepoints during pregnancy demonstrates lower risk of preterm birth with higher vitamin D closer to delivery.
abstract: There have been observational reports that maternal vitamin D status at baseline and not closest to delivery is a better predictor of pregnancy outcomes, suggesting that a cascade of events is set into motion that is not modifiable by vitamin D supplementation during later pregnancy. To address this issue, in this exploratory post-hoc analysis using correlation and logistic regression, we sought to measure the strength of the association between serum 25(OH)D concentrations at 3 timepoints during pregnancy: baseline, 1st trimester (<16 weeks); 2nd trimester (16-26 weeks); and 3rd trimester (≥27 weeks) and preterm birth. It was hypothesized that the 25(OH)D value closest to delivery would be most significantly associated with preterm birth. To accomplish this objective, the datasets from NICHD (n=333) and Thrasher Research Fund (n=154) vitamin D supplementation pregnancy studies were combined. The results of this analysis were that 25(OH)D values closer to delivery were more strongly correlated with gestational age at delivery than earlier values: 1st trimester: r=0.11 (p=0.02); 2nd trimester: r=0.08 (p=0.09); and 3rd trimester: r=0.15 (p=0.001). When logistic regression was performed with preterm birth (<37 weeks) as the outcome and 25(OH)D quartiles as the predictor variable, adjusting for study and participant race/ethnicity, as with the correlation analysis, the measurements closer to delivery were more significantly associated and had a higher magnitude of effect. That is, at baseline, those who had serum concentrations <50nmol/L (20ng/mL) had 3.3 times of odds of a preterm birth compared to those with serum concentrations ≥100nmol/L (40ng/mL; p=0.27). At 2nd trimester, the odds were 2.0 fold (p=0.21) and at the end of pregnancy, the odds were 3.8 fold (p=0.01). The major findings from this exploratory analysis were: (1) maternal vitamin D status closest to delivery date was more significantly associated with preterm birth, suggesting that later intervention as a rescue treatment may positively impact the risk of preterm delivery, and (2) a serum concentration of 100nmol/L (40ng/mL) in the 3rd trimester was associated with a 47% reduction in preterm births. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.
authors.affiliation: Medical University of South Carolina Children's Hospital, Charleston, SC, USA. Electronic address: wagnercl@musc.edu.
authors.forename: C L
authors.initials: CL
authors.lastname: Wagner
authors.affiliation: GrassrootsHealth, Encinitas, CA, USA.
authors.forename: C
authors.initials: C
authors.lastname: Baggerly
authors.affiliation: GrassrootsHealth, Encinitas, CA, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: McDonnell
authors.affiliation: GrassrootsHealth, Encinitas, CA, USA.
authors.forename: L
authors.initials: L
authors.lastname: Baggerly
authors.affiliation: Eau Claire Cooperative Health Centers, Columbia, SC, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Hamilton
authors.affiliation: Eau Claire Cooperative Health Centers, Columbia, SC, USA.
authors.forename: J
authors.initials: J
authors.lastname: Winkler
authors.affiliation: Eau Claire Cooperative Health Centers, Columbia, SC, USA.
authors.forename: G
authors.initials: G
authors.lastname: Warner
authors.affiliation: Eau Claire Cooperative Health Centers, Columbia, SC, USA.
authors.forename: C
authors.initials: C
authors.lastname: Rodriguez
authors.affiliation: Medical University of South Carolina Children's Hospital, Charleston, SC, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Shary
authors.affiliation: Medical University of South Carolina Children's Hospital, Charleston, SC, USA.
authors.forename: P G
authors.initials: PG
authors.lastname: Smith
authors.affiliation: Medical University of South Carolina Children's Hospital, Charleston, SC, USA.
authors.forename: B W
authors.initials: BW
authors.lastname: Hollis
mesh_terms: D019587:Dietary Supplements; D005260:Female; D006801:Humans; D011247:Pregnancy; D011248:Pregnancy Complications / Q000517:prevention & control*; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000517:prevention & control*; D012307:Risk Factors; D014807:Vitamin D / Q000008:administration & dosage / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood / Q000188:drug therapy*
chemical_list: D014807:Vitamin D
keywords: Cholecalciferol; Pregnancy; Preterm birth; Vitamin D