The onset of menstruation is one of several changes that occur in the female body during puberty. Menstruation, the periodic occurrence of which is commonly referred to as a menstrual period, or simply a period, occurs differently in every woman. Thus, the time and age at which a girl gets her very first period — called menarche — is a unique experience. In fact, there are a number of changes that take place before, during and after the onset of menstruation that define the experience for every girl. In general, however, young women should expect to experience other bodily changes, the possibility of having an irregular menstrual cycle, to experience symptoms associated with menstruation and to eventually develop their own unique cycle from the onset of menstruation.
Prior to the onset of menstruation, you might notice other physical and internal changes to your body, because menstruation typically starts two to three years after puberty begins. For example, before your period even arrives, you might have already begun to develop breasts or to grow hair in your pubic area and under your arms. Additionally, you might have noticed the appearance of a clear or white-colored, thick discharge that comes from the vagina. All of these events indicate that your body is getting closer to developing its menstrual cycle, signaling your fertility and ability to become pregnant. Although menstruation can begin in girls as young as 8 or 9 years old, on average, girls will get their first period when they are about 12 or 13 years old.
When menarche — your first period — occurs, it can be surprising, even if you have been expecting its arrival. The first instance of menstruation varies significantly from girl to girl. Typically, your first period will last only a few days, and the menstrual blood might appear in such a small amount that it appears to be only spotting. Furthermore, you might not have a monthly period, because it is common for many girls to have irregular periods during their first few years of menstruating. It also is possible that you will also experience cramping, bloating, headaches and irritability during or around the time of your period, because these symptoms are a reaction to the hormonal changes occurring within your body during this time.
After the onset of menstruation, the female body should naturally come into its own regular menstrual cycle, which generally will occur every 21-35 days and can last two to seven days, on average. Still, it is possible for some girls to suffer irregularities with their periods. For instance, some girls might start their periods very late into puberty, such as after age 16 years; might experience heavy bleeding, such as losing much more than the average 2 spoonfuls of menstrual blood; or have cycles that occur infrequently — such as every 90 days — or more than once a month. Furthermore, some women might have such extreme discomfort during their period that it becomes difficult to engage in their regular, daily activities. In some instances, these issues will resolve with time, but some women might require the assistance of a medical professional to treat their menstrual difficulties.