How long before a baby begins to develope?

A baby begins to develop shortly after conception, with the formation of a zygote that undergoes rapid cell division. By the end of the first trimester, significant development has occurred, including the formation of major organs and systems. By around 8 weeks, the embryo is referred to as a fetus, and further growth and maturation continue throughout the pregnancy. Overall, development is a continuous process that starts at conception and continues until birth.