Regular Menstrual Cycle

• The average length of a menstrual cycle is 28 days, starting with the first day of menstrual bleeding. For some women, the cycle is as short as 21 days or as long as 35 days.
  
  

Period Length

• A regular menstrual period can last anywhere from three to seven days.
  
  

Causes of Irregularity

• Some possible causes of an irregular menstrual cycle include pregnancy, breastfeeding, severe stress, too much exercise, excessive weight loss, eating disorders or another medical condition. Some medical conditions that might cause irregularity are polycystic ovary syndrome, pituitary tumors or thyroid disease.
  
  

Life Cycle Changes

• When a girl first begins menstruating, her cycle will often be irregular and might not become regular for several years. Women who are entering menopause also often experience irregular menstrual cycles.
  
  

Treatment Options

• In some cases of an irregular menstrual cycle, the doctor might prescribe birth control pills or another hormonal contraceptive. Other women might need supplements to adjust their hormone levels, which can help with irregularity.