Published online by Cambridge University Press: 24 December 2019
During the transition from morula to blastocyst the embryo enters the uterus, where it is sustained by oxygen and a rich supply of metabolic substrates in uterine secretions. The subsequent sequence of events that lead to implantation is a crucial milestone in mammalian embryo development. Carefully orchestrated programs are set into action, which establish diverse cell lines, specify cell fate and major remodeling that will generate the embryo and its extraembryonic tissues: during gastrulation, the three primary germ layers that lead to body formation are formed. The critical conditions that are created in this early stage will pave the way to a successful pregnancy.