The menstrual cycle relates to how a girl’s body prepares for a possible pregnancy. Hormones cause an egg to be released from the ovary and the lining of the uterus to thicken. If no pregnancy occurs, the egg and lining of the uterus break down and flow out through the vagina as a menstrual period.
Girls get their first period between the ages of 9 and 16. Don’t worry if you get your first period earlier or later than someone else, your period will start when your body is ready.
While periods usually come once a month, sometimes they can come less or more frequently. Talk to your doctor if you have any concerns about your period.