Prepregnancy habitual intakes of total, supplemental, and food folate and risk of gestational diabetes mellitus: A prospective cohort study

OBJECTIVE To identify novel modifiable risk factors of gestational diabetes mellitus (GDM) by examining the association between prepregnancy habitual folate intake and GDM risk. RESEARCH DESIGN AND METHODS The study included 14,553 women in the Nurses’ Health Study II who reported at least one singleton pregnancy between the 1991 and 2001 questionnaires. Prepregnancy intakes of total folate, supplemental folate, and food folate were assessed using a food frequency questionnaire administered every 4 years. Incident GDM was ascertained from a self-reported physician diagnosis. Relative risks (RRs) of GDM were estimated using log-binomial models, with adjustment for demographic, lifestyle, and dietary factors. RESULTS Over the study follow-up, 824 incident GDM cases were reported among 20,199 pregnancies. Women with adequate total folate intake (‡400 mg/day) had an RR of GDM of 0.83 (95% CI 0.72, 0,95, P = 0.007) compared with women with inadequate intake (