Embryo Cells Differentiate in Two Weeks

During this time, embryo cells differentiate into all the cells needed for the body's development.

Once an embryo has all of its main structures it is called a fetus.

At two weeks, the fetus is minute but has a head, sane, limb buds, and tail. It is nourished by the yolk sac.

This is the most critical stage of development; any drugs or diseases in the mother can severely damage fetuses.