Vitamin D levels linked to preterm birth

Non-white women with low levels of vitamin D are more likely to deliver preterm than white mothers, according to a new study in the American Journal of Epidemiology.

Researchers from the University of Pittsburgh Graduate School of Public Health used a random subcohort (n = 2629) from the US Collaborative Perinatal Project (1959-1965), which was augmented with any remaining cases of spontaneous preterm birth (sPTB) before 35 weeks’ gestation, resulting in 767 cases. Serum samples collected at 26 weeks or earlier were assayed for 25-hyroxyvitamin D (25[OH]D). Vascular histology and inflammatory histology constructs were created from placental pathology examinations.

No causal relationship was found between sPTB and 25(OH)D in white women. However, in non-white women, 25(OH)D serum levels of 30 to <50, 50 to <75, and ≥75nmol/L were associated with a reduction of 1.0-1.6 cases of sPTB per 100 live births. After adjusting for confounders, a 20%-30% reduction in risk of sPTB was also seen when compared with 25(OH)D levels <30 nmol/L. Inflammation-mediated cases of sPTB and sPTB cases without placental lesions were found to be the main reasons behind this association.

While the conclusions were generally supported by the study, a sensitivity analysis for unmeasured confounders suggested that some bias did exist. The authors recommended that the relationship between 25(OH)D and sPTB be studied using modern cohorts with greater emphasis on skin pigmentation and other variables.

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