Periods often occur infrequently at the beginning and at the end of a woman’s reproductive life, but this is quite normal. Many girls have infrequent periods for the first two or three years. Even though puberty has started, the ovaries take some time to mature and adolescent girls may have spells of infrequent and/or irregular periods. This is nothing to worry about and there is nothing wrong with a girl who takes a few years to establish a regular cycle.
At the other end of a woman’s reproductive life her periods may become infrequent once again. Every woman is born with all the eggs she will ever have and she makes no more. At the start of each cycle many eggs enter the race to become the egg that is ovulated, but only one egg succeeds; the others die. Regular periods depends on regular growth of an egg every month. As a woman gets older she has fewer eggs left in her ovaries. As she begins to run out of eggs a woman will ovulate less often and as a result she will begin to have irregular periods. Eventually, women stop having periods when they reach the menopause (change of life) at an average age of 51 years. Periods may become irregular and/or infrequent for eight or more years before they stop altogether. This is all perfectly normal. A woman at this stage of life is considered to be menopausal once she has had no periods for a year. Any episode of bleeding from the vagina once a woman has gone through the menopause may be an early sign of a problem and should be discussed with a doctor.
The other time in a woman’s life when her periods may come less than once every five weeks is after she has had a baby. It may be three or four months after childbirth before a woman starts to have regular periods again and if she chooses to breast-feed her baby it may be even longer than that depending on how often the baby suckles.