Sometimes infrequent periods may be abnormal. If periods have previously been regular but they become irregular (coming less often than once every five weeks, or seem to have stopped altogether) then unless the woman s approaching the menopause this may be abnormal.
Some women never develop a regular cycle. If after four years or so after a woman starts her periods they are still coming infrequently, then this may be abnormal. Regular periods are caused by the shedding of the lining of the womb which is dependant on the regular development of the egg. If for some reason a woman produces eggs less frequently than once a month, then her periods will come less often. The control of the menstrual cycle is very complicated and a very minor hormone imbalance can cause infrequent periods or even switch them off altogether. Hormones produced in the brain and pituitary gland stimulate the growth of the egg in the ovary.
The hormones produced by the ovary as the egg develops (estrogen and progesterone) stimulate the growth of the lining of the womb. The balance between these hormones and the precise pattern of their release into the bloodstream are important for the maintenance of normal regular ovulation and menstruation. Minor abnormalities of the pattern of release of these hormones can upset the entire system and cause infrequent periods.