A menstrual cycle is the time from the day a menstrual period starts to the time the next period starts. The average menstrual cycle is 28 days long. However, a normal cycle can be shorter or longer than this. It may be anywhere from 21 to 35 days long. Most periods last 3 to 5 days, but anywhere from 2 to 7 days is normal. Menstrual cycles may happen around the same date every month or they may be irregular.
A menstrual period is considered late if it hasn’t started 5 or more days after the day you expected it to start. A period is considered missed if you have had no menstrual flow for 6 or more weeks after the start of your last period.
During the first couple of years of menstruation many teenagers have irregular periods. During this time your body is still developing and the ovaries may not release an egg every month. As a result, your cycles may be irregular, occurring as close together as 2 weeks or as far apart as 3 months. If you have been having periods for 2 years or less and your physical exam is normal, your irregular periods may be part of your normal development.
Most girls' menstrual cycles become fairly regular as their hormone levels mature and synchronize. A few women will continue to have irregular cycles as their normal pattern.
Other causes of a late or missed period are:
Pregnancy is the most common cause of missed periods in teenage girls. If your period is late and you have had sex even once in the past several months, see your healthcare provider. It’s best to see your healthcare provider for a pregnancy test because home test kits can be confusing and give incorrect or unclear results.
It is important to find out early if you are pregnant. Starting prenatal care right away helps you have a healthy baby.
If you are pregnant, you will not have a normal period until after the baby is born.
Stress is the second most common cause of late or missed periods in teenagers. It may be emotional stress (for example, breakup with a boyfriend or final exams) or depression. Or it may be physical stress to the body, such as a severe illness, a sexually transmitted disease, rapid weight loss or gain, or strenuous exercise. Dieting or binging and purging may interrupt menstrual cycles. Changes in your usual routine (for example, going on vacation) may also cause your period to be late or missed.
Some stress is a normal part of daily life. Too much stress for your body may cause a late or missed period. Your periods should come back when you change your activities or situation.
In some cases hormone imbalance is causes missed periods. For example, if you have been taking birth control pills, your periods may be irregular for a while when you stop taking the pills. If you are having sex, be sure to use another reliable method of birth control because you could still get pregnant.
A rare problem called polycystic ovary syndrome can affect a young woman’s menstrual cycle. Polycystic ovaries may cause irregular cycles, more body hair, acne, and weight gain. It can be treated with hormone medicine prescribed by your healthcare provider.
Problems of the thyroid gland, pituitary gland, adrenal glands, or ovaries are other rare causes of irregular periods.
Talk with your healthcare provider if you are not sure what your proper weight should be, or if others are worried about your weight. A nutritionist may also be able to give you helpful advice.