Some girls don't experience any signs prior to a first menstrual period except when the actual bleeding or spotting starts, while others will experience premenstrual symptoms similar to those that will occur later in life. These can include mood swings or irritability, fatigue, and bloating; some girls will also notice changes in their skin, or that they are more prone to developing blemishes before the first period. The age of a first menstrual period, known as menarche, can vary depending on a number of factors. Some girls experience it as early as age 8 or 9, while others may not get it until they are 13 or 14; the most common ages are 11 and 12.
The first menstrual period can usually be anticipated based on other signs in the body. This is because menstruation usually begins roughly two years after puberty first starts, which is typically indicated by the first appearance of breasts. Many young girls will also experience a growth spurt around this time as well. There are no rules or absolutes, however, and the first menstrual period can really appear at any time for girls once they have reached puberty.
Because of the nature of the first menstrual period, there are typically not many other physical signs that precede it, and it is often a surprise. Some girls will experience stomach cramps or bloating, however, while others will notice mood changes. They might feel more emotional or more irritable than usual, which can be a good indication. Some might be especially tired, or notice appetite changes. These signs will typically appear just a few days before menstruation begins, and are generally quite similar to PMS symptoms that are experienced by adults with regular menstrual cycles.
A first menstrual period will typically be fairly short. Many girls experience irregular cycles for quite a while after the first one, sometimes even for a few years. This means that the length of time in between cycles can be longer or shorter than the 28-day average, or even that a month is skipped here and there. Any girl who is sexually active at this point, and skips a period, should be aware that pregnancy is possible. Each girl matures differently, and some will experience regular menstrual cycles right away, while some women will experience irregular cycles throughout their whole lives; it is impossible to predict, so it is important to keep track of the cycle each month once it begins.