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. It is also normal for girls to feel nervous or scared when they start getting their periods. The time from the first day of one period to the first day of the next is called a menstrual cycle. On average, menstrual cycles begin between the ages of 12 and 13.