Fish consumption more than once a week during pregnancy as well as during the child’s first year of life was associated with an increased risk of JIA (aOR 4.5 (1.95–10.4); p < 0.001 and aOR 5.1 (2.1–12.4) p < 0.001) and of ANA-positivity (aOR 2.2 (1.4–3.6); p = 0.002 and p < 0.001). This evidence concerns the gene BTG3 and juvenile idiopathic arthritis.