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Human Reproduction

Biological Basics and Terminology


As the egg, or ovum, progresses through the fallopian tube toward the uterus, it secretes a special substance to help signal its location to any sperm which may have been released by a man during sexual intercourse. Millions of sperm are ejected by the man, but only one sperm penetrates the egg, leading to pregnancy. This process, called fertilization, is the point at which a new human life is formed.
The developing child is given its own unique set of DNA--half from each parent. The DNA is like a blueprint which determines the child's physical characteristics and many other traits as well. The embryo will then travel down to the uterus where it implants in the uterine lining and begins to grow. At the moment of implantation, a woman is officially considered pregnant in medical terms, although the embryo is very much alive before this point.

Traditionally, the words "fertilization" and "conception" were synonymous, and lay people still use the word conception to refer to the moment at which the egg and sperm join. However, in recent years, several medical organizations have pushed to change the definition of conception to mean implantation instead of fertilization. This site will use the term "fertilization" to avoid any ambiguity.

Although a woman is only fertile for a few days out of each menstrual cycle, unless she is monitoring her body it is hard to know exactly when she can get pregnant. Couples who want to prevent pregnancy must either refrain from intercourse during the fertile time or make use of artificial contraceptives. Both natural and artificial means of birth control are described at this web site.

When does Ovulation Occur?

Every woman's cycle is different, but with some close attention most women can determine what their cycle is like and when pregnancy can occur. Fertilization is most likely to occur if couples have intercourse near the time of ovulation. For women with regular cycles, ovulation is expected to occur about fourteen days from the first day of menstruation, but variations are common.

Sperm can survive for several days inside of a woman, residing safely in the fallopian tubes or within spaces in the cervix. Although most sperm die within three days, they have been known to survive for as long as a week under certain conditions. Once released, an egg can survive for twenty-four hours. The fertile period is from two to three days before, to one day after, ovulation. It is important to remember, however, that your fertile period may not occur at the same time each month. Ovulation can be delayed by changes in diet, stress, travel, or other factors.

When Does Life Begin?

A new human life begins at the moment of fertilization. Click the arrow below to learn more about the amazing process of human development.

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