Official German recommendations advise women to start taking folic acid supplementation (FAS) before conception and continue during the first pregnancy trimester to lower the risk of birth defects. Women from lower socio-economic background and ethnic minorities tend to be less likely to take FAS in other European countries. As little is known about the determinants of FAS in Germany, we aimed to investigate the association between FAS and formal education and migration background, adjusting for demographic factors. We used data (2013-2016) on nutrition and socio-economic and migration background from the baseline questionnaire of the BaBi cohort study. We performed multivariate regressions and mediation analyses. Bielefeld, Germany. Nine-hundred forty-seven women (pregnant or who had given birth in the past 2 months). 16.7% of the participants (158/947) did not use FAS. Migration-related variables (e.g. language, length of stay) were not associated with FAS in the adjusted models. FAS was lower in women with lower level of formal education and in unplanned pregnancies. Reasons given by women for not taking FAS were unplanned pregnancy and lack of knowledge of FAS. Health practitioners may be inclined to see migrant women as an inherently at-risk group for failed intake of FAS. However, it is primarily women who did not plan their pregnancy, and women of lower formal education level, who are at risk. Different public health strategies to counter low supplementation rates should be supported, those addressing the social determinants of health (i.e. education) and those more focused on family planning.