Some Facts About Eggs

At birth, a woman's ovaries contain up to 472,000 immature ova (eggs). The years between puberty and menopause are considered a woman's reproductive years. During these reproductive years, about 400 eggs are destined to become fully mature. Typically, the left and right ovaries take turns every other month to release one egg during each menstrual cycle.

After an egg is released from the ovary, it travels through the nearby fallopian tube and into the uterus (click here for a diagram). While in the fallopian tube, the egg moves along at a rate of about 1 inch every 24 hours. It is in the fallopian tube that the egg has the potential to be fertilized by a man's sperm. The time period during which an egg can become fertilized in the fallopian tube is about 24 to 48 hours. If the sperm and egg meet, and the egg does become fertilized, it will continue to develop into a zygote which later develops into a fetus, once it reaches the uterus.

During the egg's journey from the ovary to the uterus, the inner lining of the uterus is busy building up extra tissue and blood, in case the egg that arrives has been fertilized and is ready to implant in the uterus, where it will continue to develop into a fetus. The implantation of a fertilized egg usually occurs about 1 week after fertilization.

If the egg has not been fertilized it will degenerate and become re-absorbed by the body. The extra blood and tissue that the uterus has created will be unnecessary, and it will leave the body through the vagina, during the process called menstruation, or a woman's "period."