From Fertilization to the Birth of the Baby

At the man's climax in intercourse, millions of sperm cells, swimming in semen, are ejaculated from his penis into the woman's vagina near the mouth of the cervix. At once, these microscopic sperm, their tails moving rapidly back and forth, begin a journey that takes from one to several hours. In their warm, moist environment, the sperm normally stay alive and are capable of fertilizing the egg cell for two-and-a-half to three days, although sperm may be actively moving as long as a week after they are ejaculated.

Sperm appear to have no sense of direction, and ofcourse they cannot see. They move about rapidly in a random motion, not on a direct route. Some make their way up through the cervix into the uterus. Some of these enter the two fallopian tubes. They proceed up the tubes, where they may meet a mature egg cell travelling slowly in the opposite direction. If they do, they croud around the ovum and bombard its wall until it weakens at one spot just enough to permit a single sperm cell to enter.

At once the cell wall hardens and the other sperm are shut out; the successful one loses its tail; its head joins the nucleus of the egg. The rest of the sperm cells die and are absorbed harmlessly into the woman's body. The moment of joining of sperm and egg is called fertilization or conception; new life is conceived, that is to say, begun. It is important to understand the fertilization will not occur every time a man and woman have intercourse; far from it.

The sperm must arrive in the fallopian tube just when an egg is travelling through it. The sperm must be vigorous and the egg not too ole - that is, not more than twelve to twenty-four hours out of the ovary. It is the sperm cell that determines whether the child is to be a boy or a girl.

The sex depends on which of two types sperm cells enters the ovum. If it is sperm carrying a "Y'' chromosome, the baby will be a boy; if it is an "X'' chromosomem, it will be a girl. Nothing that happens to the mother after fertilization can change the sex of the baby.