3'‑FL is a trisaccharide formed of L-fucose linked with lactose (Gal β1‑4 (Fuc α1‑3) Glc) (Kunz et al. 2000). 3'‑FL is one of the most abundant oligosaccharides in human milk. Its expression is genetically regulated and important to define milk groups (Kunz et al. 2017). Lewis blood group gene, secretor gene, fucosyltransferase.