Early-Pregnancy Vitamin D Deficiency and Risk of Preterm Birth Subtypes

Study answer

What this study found

Higher early-pregnancy 25(OH)D status is associated with lower risk of preterm birth. Adjusted risk for preterm birth <37 weeks: <50 vs ≥75 nmol/L: 1.8 (1.3–2.6); 50–74.9 vs ≥75: 1.4 (1.1–1.8). For preterm birth <34 weeks: <50 vs ≥75: 2.1 (1.3–3.6); 50–74.9 vs ≥75: 2.2 (1.4–3.4). Risk declines as 25(OH)D rises to ~90 nmol/L and then plateaus. Findings are similar for spontaneous and indicated preterm birth and do not vary by race/ethnicity. Conclusion: Vitamin D sufficiency in early pregnancy is associated with lower preterm birth risk; these observational data support conducting…

Study & population

Case-cohort study (EVITA) of pregnant women delivering singleton live-born infants at Magee-Womens Hospital, Pittsburgh.

Key limitation

Observational design limits causal inference; potential residual confounding; serum 25-hydroxyvitamin D measured once in early pregnancy and reflects total, not bioavailable, vitamin D; lack of additional vitamin D metabolism markers (e.g., binding protein) and detailed phenotypic data; generalizability may be…

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Original abstract