Pregnancy
Fertilization of the egg takes place within the fallopian tube. As the fertilized egg passes down the tube, it undergoes its first mitotic divisions. By the end of the week, the developing embryo has become a hollow ball of cells called a blastocyst. At this time, the blastocyst reaches the uterus and embeds itself in the endometrium, a process called implantation. With implantation, pregnancy is established.

The blastocyst has two parts:
the inner cell mass, which will become the baby, and
the trophoblast, which will
develop into the placenta and umbilical cord
and begin to secrete human chorionic gonadotropin (HCG).

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