A "regular" menstrual cycle varies from woman to woman and lasts as long as 24 to 35 days, with a period lasting anywhere between 4 to 7 days. Once the normal baseline has become established, she can then determine that her period is irregular based on an absence of a period, experiencing long-lasting or abnormally heavy periods. According to the McKinley Health Center of the University of Illinois at Urbana-Champaign, underlying physical and hormonal imbalances cause the occurrence of irregular menstrual cycles, affecting over 30 percent of women in their reproductive years.
Stress
Both physical and emotional stress can shift the hormonal balance and cause a menstrual cycle to become irregular. According to the Epigee website, mental or emotional stress such as feeling anxious, worrisome and becoming overly fatigued can negatively affect a woman's hormones. Physical stress in forms of illness, extreme weight loss and gain, as well as intense exercise has a similar hormonal effect. The body also becomes stressed under physical conditions resulting from poor nutrition, such as anorexia or bulimia, thus causing irregular or absent periods.
Physical Conditions
Under normal circumstances when the body remains free of an underlying disorder, women experience irregular periods due to several physical conditions. Adolescents who have just begun their periods often experience irregularity until the menstrual cycle becomes established. The Epigee website states it may take up to three years for the cycle to become regular. Pregnancy and menopause are other normal reproductive conditions characterized by absence of periods as a result of hormonal changes. According to Discovery Health, breastfeeding women also commonly experience menstrual fluctuations as do those who recently stopped taking birth control pills.
Underlying Complications
For the majority of women, menstrual irregularity is fleeting and the menstrual cycle settles into a routine with time. However, for others, there may be underlying complications that cause abnormal periods and bleeding. According to Medline Plus, a service of the National Institutes of Health, polycystic ovary syndrome, pelvic inflammatory disease, endometrial hyperplasia and uterine cancer are some of the conditions to blame. Other medical disorders that may affect a woman's menstrual cycle include thyroid and pituitary problems, diabetes, cirrhosis and inflammatory bowel disease.
