Histotroph is the complex mixture of molecules secreted into or transported into the uterine lumen. Histotroph includes nutrient transport proteins, ions, mitogens, cytokines, lymphokines, enzymes, hormones, growth factors, proteases and their inhibitors, amino acids, glucose, fructose, vitamins, and other substances. Histotroph is a primary source of nutrition for mammalian conceptus development. In humans, its importance continues throughout the first trimester of pregnancy until hematotrophic nutrition is established.