According to WebMD, a missed menstrual period commonly indicates pregnancy. If pregnancy isn't the cause, then it can be due to weight gain or loss, eating disorders, emotional stress, illness, increased exercise, travel, hormone problems, breastfeeding, birth control or illegal drug use.
WebMD states that irritable bowel syndrome, tuberculosis, liver disease and diabetes can cause missed or irregular periods. However, this is rare. If any of these diseases are present, they are accompanied by other symptoms besides menstrual irregularities. Many women miss periods every once in a while. When a skipped period occurs, restoring emotional and physical balance can help. Except in the case of a pregnancy, the cycle most likely returns to normal within the next month.
WebMD notes that most women have between 11 and 13 menstrual periods each year, although some women may have fewer periods. Because every woman is different, missed or irregular periods must be considered in terms of what is normal for each individual woman. During the first few years after menstruation begins, periods are often irregular. It can take several years before the hormones that control menstruation reach a balance. Menstrual periods may be very irregular toward the end of menstrual years, which indicates that menopause is approaching. Menopause occurs when it has been 12 months since a menstrual period has occurred.