Maternal postpartum plasma folate status and preterm birth in a high-risk US population

Objective While maternal folate deficiency has been linked to poor pregnancy outcomes such as neural tube defects, anaemia and low birth weight, the relationship between folate and preterm birth (PTB) in the context of the US post-folic acid fortification era is inconclusive. We sought to explore the relationship between maternal folate status and PTB and its subtypes, i.e. spontaneous and medically indicated PTB. Design Observational study. Setting Boston Birth Cohort, a predominantly urban, low-income, race/ethnic minority population at a high risk for PTB. Participants Mother-infant dyads (n 7675) enrolled in the Boston Birth Cohort. A sub-sample (n 2313) of these dyads had maternal plasma folate samples collected 24-72 h after delivery. Results Unadjusted and adjusted logistic regressions revealed an inverse relationship between the frequency of multivitamin supplement intake and PTB. Compared with less frequent use, multivitamin supplement intake 3-5 times/week (adjusted OR (aOR) = 0 center dot 78; 95 % CI 0 center dot 64, 0 center dot 96) or >5 times/week (aOR = 0 center dot 77; 95 % CI 0 center dot 64, 0 center dot 93) throughout pregnancy was associated with reduced risk of PTB. Consistently, higher plasma folate levels (highest v. lowest quartile) were associated with lower risk of PTB (aOR = 0 center dot 74; 95 % CI 0 center dot 56, 0 center dot 97). The above associations were similar among spontaneous and medically indicated PTB. Conclusions If confirmed by future studies, our findings raise the possibility that optimizing maternal folate levels across pregnancy may help to reduce the risk of PTB among the most vulnerable US population in the post-folic acid fortification era.