Infrequent or Irregular Periods

What are periods?
The control of a woman’s reproductive cycle is complicated. The cycle is designed so that a woman produces an egg once each month, allowing her the possibility of becoming pregnant. Each cycle begins with the first day of the period. A number of eggs begin to grow in the ovary until, after fourteen days, one egg is mature enough to be released from the ovary (ovulation). While developing, the cells around the egg produce the hormone oestrogen. After ovulation these cells produce a second hormone, progesterone. Together the two hormones stimulate the lining of the uterus (womb) to grow. The ovulated egg enters the fallopian tube and travels towards the womb. If intercourse has taken place and no contraception has been used, the sperm may fertilise the egg while it is in the tube. The resulting embryo will implant into the lining of the womb where it develops into a baby.
The human race is not very fertile. It has been calculated that a woman who is not using contraception has on average only a 28 % chance of conception each cycle. If the egg is not fertilised, it does not implant. Fourteen days after ovulation the lining of the womb, together with some blood, is shed into the vagina and the whole process starts all over again.
The shedding of the lining of the uterus is the period or ‘menstruation’. Most women have a period once each month. The cycle length, (the start of one period to the start of the next), varies among individuals, but anything between 21 and 35 days is considered normal. Of course an individual woman’s cycle will vary from month to month by two or three days, but this is also normal.
Some women have periods that come less often than once every 15 weeks, i.e. they bleed infrequently. Gynaecologists call this condition oligomenorrhoea – oligo means few and menorrhoea essentially means having periods. If you have not had a period for a long time the term amenorrhoea (no periods) is used.
Infrequent periods that are normal
Periods often occur infrequently at the beginning and at the end of a woman’s reproductive life. This is quite normal. Many girls have infrequent, heavy or irregular 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 makes it. The other eggs then die. As a woman gets older she has fewer eggs left in her ovaries. It is the regular growth of an egg each month that results in regular periods. As she begins to run out of eggs a woman will ovulate less often. As a result she will begin to have irregular and more frequent 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. If she chooses to breast-feed her baby, it may be even longer than that depending on how often the baby suckles.
Infrequent periods that may be abnormal
Unless you are approaching the menopause, infrequent periods may be abnormal if:

1. you have previously had regular periods but they become irregular (coming less often than once every five weeks), or seem to have stopped altogether;
2. after four years or so after starting your periods, they are still coming only infrequently (some women never develop a regular cycle).

It is the regular development of the egg followed by the shedding of the lining of the womb that causes regular periods. If, for some reason, you are producing eggs less frequently than once a month, your periods will come less often.
The control of the menstrual cycle is very complicated. 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 (oestrogen 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. It is interesting that nothing else seems to go wrong. The control of regular ovulation and periods seems to be a particularly sensitive bodily function. It may be nature’s way of making sure that a woman is less likely to get pregnant when she is not in the best shape for having a baby and looking after a child.