The first two weeks after conception are called the pre-embryonic period.
Week One
The sperm and egg come together through fertilization to form the zygote. Over the next several days, rapid cell division allows the zygote to develop into a pre-embryo. During this time, the pre-embryo-a ball of cells-travels from the fallopian tube to the uterus. Six to seven days after fertilization, the pre-embryo implants into the endometrium (lining of the uterus).
Week Two
At this point, further cell division and differentiation allows the pre-embryo to enlarge into an embryonic disc. A yolk sac forms, which provides early nutrition for the embryo. The beginnings of the placenta, called chorionic villi, also begin to develop at this time.
