Background: Folate, vitamin B-12, and homocysteine concentrations during pregnancy are important factors for early development and may persistently influence kidney function in the offspring. We examined the associations of folate, vitamin B-12, and homocysteine concentrations during pregnancy with kidney outcomes, in school-aged children. Study Design: Population-based prospective cohort study from fetal life onward. Settings & Participants: This study was performed among 4,226 pregnant women and their children. Predictors: Folate, vitamin B-12, and homocysteine blood concentrations measured in early pregnancy (median gestational age, 13.2 [IQR, 12.2-14.8] weeks) and at birth (cord blood). Outcomes & Measurements: At the median age of 6.0 (IQR, 5.9-6.3) years, we measured combined kidney volume with ultrasound, estimated glomerular filtration rate based on creatinine (eGFR(cr)) and cystatin C (eGFR(cys)) concentrations, and microalbuminuria. Results: We observed that higher maternal folate concentrations were associated with larger childhood combined kidney volume, whereas higher maternal vitamin B-12 concentrations were associated with higher childhood eGFR(cys) (P for both <0.05). These associations were independent of homocysteine concentrations. Higher maternal homocysteine concentrations were associated with smaller combined kidney volume and lower childhood eGFR(cys) (P for both < 0.05). The association of maternal homocysteine concentrations with childhood eGFR(cys) was largely explained by combined kidney volume. Higher cord blood homocysteine concentrations were associated with larger combined kidney volume and lower eGFR(cys) (P for both < 0.05). Folate, vitamin B-12, or homocysteine concentrations were not associated with microalbuminuria. Limitations: Observational study, so causality cannot be established. Conclusions: Our findings suggest that folate, vitamin B-12, and homocysteine concentrations during fetal life are associated with offspring kidney development. However, effect sizes are small. Further studies to replicate these findings and assess the causality and consequences for kidney health in later life are needed. (C) 2017 by the National Kidney Foundation, Inc.