Maternal periconception serum vitamin B12 concentration and risk of preterm birth: a prospective cohort study.

Background: Maternal vitamin B12 levels during pregnancy have been implicated in the risk of preterm birth, but current evidence remains controversial and just focuses on measurements during pregnancy.

Objective: To assess the association of maternal periconception serum vitamin B12 concentration, including levels before conception and at early gestation, with the risk of preterm birth and its subtypes in a large Chinese population.

Design: Prospective cohort study.

Participants: A total of 26 977 women from Shanghai, China, with serum vitamin B12 concentration measured either before conception or at early gestation.

Outcome measures: Preterm birth was defined as delivery before 37 weeks of gestation and was stratified as preterm birth <32 and <34 weeks. Cox regression was used to estimate the association between maternal vitamin B12 and preterm birth.

Results: Overall, 1599 (5.9%) of participants delivered preterm. The median periconception vitamin B12 concentration was 483.0 (IQR, 368.0-622.0) pg/mL. No evidence was observed of an association between maternal vitamin B12 concentration and risk of preterm birth (per 100 pg/mL increment: adjusted hazard ratio (aHR), 0.99; 95% CI, 0.96 to 1.02, P=0.572). Similarly, null associations were observed for preterm birth subtypes (aHR, 0.98 [0.89 to 1.09] and 0.97 [0.90 to 1.05] for preterm birth <32 and <34 weeks, respectively).

Conclusions: No evidence of associations was found between maternal vitamin B12 concentration and risk of preterm birth in a population with relatively sufficient vitamin B12 levels. Future studies in populations with varied baseline levels of vitamin B12 are needed to validate these findings across different populations and regions.