Association between folic acid use during pregnancy and gestational diabetes mellitus: Two population-based Nordic cohort studies.

The slightly higher or lower odds for GDM in self-reported users of folic acid in Norway and Sweden respectively, are likely not of clinical relevance and recommendations for folic acid use in pregnancy should remain unchanged. The two Nordic cohorts showed different directions of the association between self-reported folic acid use and GDM, but based on bias analysis, exposure misclassification is an unlikely explanation since there may still be differences in prevalence of use and residual confounding. Prescribed folic acid is used by women with specific comorbidities and co-medications, which likely underlies the higher odds for GDM.