The Developing Baby: Week 1-2 Health Article

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.

For more information, go to The Developing Baby: Week 3-8 and The Developing Baby: Week 9-12.