When does the fetus start to grow after egg has been fertilized?

The term fetus is used to describe the developing human from 8 or 9 weeks after fertilization of the egg, once the major organs and body structures have formed.

Prior to this, from the moment of fertilization to 8 or 9 weeks the developing human is referred to as an embryo. The embryo stage encompasses the processes of cell division, cell migration, and cell differentiation that create the basic body structures. As these structures become fully formed and recognizable as the blueprint of a human, the developing human then transitions from being an embryo to a fetus.