1. Zygote: As the zygote moves down the fallopian tube, it duplicates, at first slowly then more rapidly
2. Blastocyst: By the fourth day it forms a hollow, fluid-filled ball called a blastocyst. The inner cells, called the embryonic disk, will become the new organisim. The outer cells or trophoblast will provide protective covering.
3. Implantation: At the end of the first week, the blastocyst begins to implant in the uterine lining.
Female reproductive organs:
Periods of Prenatal Development
Period Length Key Events
Zygote - 2wks - Fertilization, Implantation and start of placenta