Conception
Fertilization is the first step in creating a new human being. During fertilization, a sperm swims through the uterus and into the fallopian tubes, where it meets with an egg. The two combine to form a zygote, a cell that contains the 46 chromosomes necessary to form a human being. The zygote then travels back downwards to the uterus, dividing itself into a group of several cells along the way. About six to 12 days after fertilization, the zygote will make its way to the wall of the uterus and implant itself.
Embryo
When the zygote implants itself into the wall of the uterus, it becomes an embryo. At this point, the cells begin to transform into rudimentary organ systems. The heart starts beating, and a simple tube is the beginning of the nervous system. Over time, the organs become more and more specialized. Arms and legs begin to form and the embryonic tail is absorbed into the growing body. The brain, lungs, liver, kidneys take shape. Six weeks after fertilization, the embryo has now developed into a fetus. It is still only 1 inch in size.
Fetus
The fetal stage is the longest stage of pregnancy, stretching from six weeks after fertilization all the way to birth. When an embryo becomes a fetus, it has the basis for all its main organ systems. At this point, the fetus' outward appearance becomes more human. Hair, eyebrows and finger and toenails appear, and fat is stored in the body. The genitalia form. The muscles develop to the point where the mother can feel the fetus' movements. The fetus begins human activities, such as sleeping and breathing. Late in pregnancy, the fetus turns in the womb, so its head faces the vaginal canal. He is now almost ready to be born.
