First Week of Development

Fertilization occurs when a sperm and an egg have fused together to form a zygote, which begins to divide as it moves towards the uterus.

The process of cleavage is the step of embryogenesis where the zygote divides to produce a cluster of cells known as the morula.

The blastocyst forms early in embryonic development and has two layers that form the embryo and placenta.

Implantation is the very early stage of pregnancy at which the embryo adheres to the wall of the uterus and begins to form the placenta.