A new article published in BIO Integration on July 15 reports that current evidence does not support universal vitamin D supplementation during pregnancy to prevent preterm birth. The study addresses ongoing controversy regarding the association between prenatal vitamin D supplementation and risk of preterm birth, drawing from randomized controlled trials.
Researchers conducted a comprehensive search of PubMed, Web of Science, Medline, Cochrane Library, and Embase up to April 2023 without language restrictions. They included randomized controlled trials comparing vitamin D supplementation with placebo, no treatment, or standard low-dose vitamin D (600 IU/day or less) in pregnant women. The primary outcome was preterm birth before 37 weeks' gestation; secondary outcomes included maternal adverse events and neonatal anthropometric indicators.
The analysis incorporated thirty-eight randomized controlled trials involving 17,392 pregnant women. Of these studies, nineteen trials involving 7,959 participants reported on preterm birth. The findings indicated that vitamin D supplementation was associated with a borderline increase in the risk of preterm birth in the primary analysis (relative risk 1.13; confidence interval 1.01-1.26; P = 0.04), though this result was largely influenced by one large trial among women living with HIV.
Exploratory subgroup analyses showed an increased signal for preterm birth among participants with baseline serum 25(OH)D levels at or above 30 nmol/L (odds ratio 1.25; confidence interval 1.05-1.48). However, this finding originated entirely from the same HIV-positive population trial and did not extend to healthy pregnant women or other subgroups based on dose or timing of supplementation initiation.
No significant effects were observed for maternal or neonatal secondary outcomes across the studies reviewed. Limitations cited include incomplete reporting of preterm births across some trials and reliance on results from a single population-specific trial for certain findings.
The authors conclude that "current evidence does not support universal vitamin D supplementation to prevent preterm birth." They caution that any possible increased risk among those with higher baseline vitamin D status should be interpreted carefully, as it is based solely on data from one specific group.
