Fertilization of an egg by a sperm occurs in the oviduct.

The resulting zygote begins several rounds of cell division without growth in a process called cleavage.

Division of cells gives rise to a blastocyst, a ball of cells with a cavity.

The blastocyst implants in the wall (endometrium) of the uterus.

The outer layer of the blastocyst (trophoblast), together with the endometrium, forms the placenta.