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

Abstract

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. 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. Prospective cohort study. A total of 26 977 women from Shanghai, China, with serum vitamin B12 concentration measured either before conception or at early gestation. 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. 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, <i>P</i>=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). 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.