Irregularities in the menstrual cycle may be caused by a variety of conditions, including pregnancy, eating disorders, ovarian failure, uterine fibroids and pelvic inflammatory disease, according to Mayo Clinic. Additionally, changes in body weight or contraception may change the menstrual cycle.
The regularity and frequency of a menstrual cycle is different for each woman, and it's important that a woman determine her regular menstrual cycle by tracking the start and end dates each month, according to Mayo Clinic. Generally, the cycle may occur every 21 to 35 days, but the cycles are often longer for younger women and shorten with age. Cycles may last from two to seven days, and they may or may not start at a regular time each month. Other variables include the heaviness or lightness of flow as well as any accompanying discomfort or pain.
Changes in a menstrual cycle aren't usually serious, but they may indicate an underlying health condition, according to Mayo Clinic. Pregnancy and breast-feeding are common causes of an interruption in the cycle. Anorexia nervosa, extreme weight loss or intense exercise can also cause a change or disruption in the frequency. Additionally, noncancerous growths, infection of the reproductive organs or malfunction of the ovaries can initiate irregularity.
Many irregularities can't be prevented, but birth control pills sometimes normalize the cycle, reports Mayo Clinic. A woman should consult her doctor if she experiences increased pain, if bleeding is heavier than normal, there is bleeding for more than seven days or there is no bleeding for more than 90 days.