Different women have different amounts of flow during their periods. About only three or four tablespoonfuls of it are blood - although it may seem like more. But the egg doesn't always break apart. If the egg meets a sperm in the fallopian tube, they can join together. The joining of the egg and sperm is called fertilization.
Pregnancy begins if a fertilized egg attaches itself to the lining of the uterus.
The lining stays in place until the pregnancy ends. That s why pregnant women do not have periods. Some families celebrate menarche as the time when a girl becomes a woman. Other families are more private about it. But whether or not menarche is celebrated, it is an exciting and important moment in a girl's life.