Changes in the menstrual cycle can result from taking contraception, eating disorders, stress, lack of sleep, or a sharp increase in exercise, among many other factors, according to WebMD. Other factors that can affect a woman's menstrual cycle include pregnancy, breastfeeding, polycystic ovary syndrome, pelvic inflammatory disease and uterine fibroids, according to the Mayo Clinic.
According to WebMD, normal menstrual cycles range anywhere from 21 to 35 days, with the average period lasting three to five days. Women typically experience differences in their flow throughout their lifetime. While younger women tend to have longer, heavier periods, as a woman ages, her periods become shorter and more regular.
If a woman's menstrual cycle is regularly infrequent, she may otherwise be healthy and simply have an irregular menstrual cycle naturally. The menstrual cycle is controlled by hormonal fluctuations. It is more important to track when and how often changes occur rather than the changes themselves in order to determine if a problem exists. A woman taking birth control bills will experience changes in the menstrual cycle. WebMD reports that middle-aged women experiencing significant changes to or a stoppage in their menstrual cycle may be experiencing the early stages of menopause. If periods have stopped completely in younger women, pregnancy could be the cause.