Fertilization occurs in the Fallopian tube. If the egg is not fertilized within 24 hours after it is released, it travels down to the uterus and is expelled during the menstrual period.
Once a month, egg cells start to ripen. On each ovary, many egg cells start to ripen each month. Only one egg cell matures and is released, or sometimes one from each ovary. The rest of the ripening egg cells deteriorate. Some women experience abdominal pain on one side when the ripe egg cell ruptures from the ovary. This is called mittelschmerz, and is sometimes accompanied by light spotting, the Mayo Clinic reports. After rupturing from the ovary, the ripe egg cell is passed to the Fallopian tube, where it stays for 12 to 24 hours. It is here that the egg is met by a sperm cell and fertilized. After fertilization, it rapidly divides many times and begins to travel down the Fallopian tube to the uterus.
Once the fertilized egg makes it to the uterus, it burrows into the lining. This is called implantation. Some women experience a small amount of spotting that lasts one or two days following implantation. This is known as implantation bleeding, and occurs about a week before the woman's expected period. It does not happen to all women, but it does not indicate a problem, according to WebMD.