What is menstruation?

Menstruation, or having periods, is part of the female reproductive cycle. Menstruation results from the regular shedding of the lining of the womb (endometrium) and some blood in a woman who is not pregnant.

While the average interval between periods is 28 days, many women will have cycles that are either longer or shorter than this. Ninety-five per cent of women will have a menstrual cycle between 24 and 35 days long. The length of bleeding also varies from one to eight days, with the average length being five days.

What happens during menstruation?

The female internal sex organs consist of the ovaries, the fallopian tubes, the womb and the vagina.

A woman is born with eggs already in her ovaries. A single egg usually matures each cycle and this process is accompanied by a thickening of the lining of the womb (endometrium) in preparation for implantation, if pregnancy occurs.

If however the egg is not fertilised, hormonal changes take place which result in the endometrium breaking down. It is shed during a menstrual period.

The menstrual discharge is therefore made up of the endometrium that has broken away and some blood. This blood is caused by the breaking of tiny blood vessels within the endometrium as it breaks away from the womb.

The actual amount of blood loss varies from cycle to cycle and from woman to woman but is usually less than 80mls for any one period.

What are the four stages of the menstrual cycle?

The first stage of the menstrual cycle is the actual period. The first day of the period is known as Day 1 of the cycle. For most women this lasts between three and seven days.

The second stage starts towards the end of the period. One of the two ovaries begins to prepare an egg (also known as an ovum), which will eventually be released into the fallopian tubes. The lining of the endometrium starts to thicken in preparation for the egg. These actions are promoted mainly by rising levels of the hormone oestrogen.

The third stage is known as ovulation. It happens around midcycle (day 14 of a 28 day cycle). A mature egg is released from the ovary and enters the fallopian tube.

The fourth stage sees the egg journeying down the fallopian tube towards the womb, while the endometrium continues to thicken. This proliferation of the lining of the endometrium results from the rising levels of the hormone progesterone which is triggered by ovulation. If the egg is not fertilised by a sperm at this stage, it disintegrates and the endometrium starts to break away, starting the whole cycle all over again.

When does menstruation start and finish?

A girl starts menstruating at the time of puberty. This is usually between the ages of 11 and 16. However some girls begin having periods before the age of 11 or after the age of 16. There is usually no reason for concern when this happens, however if you are worried or anxious, you may wish to talk to an adult such as a parent or the school nurse, to put your mind at ease.

A woman will continue menstruating until her menopause. This usually occurs when the woman is in her late 40s or early 50s. Like the first period, these ages are not definite. Some women experience menopause at a younger age, some at an older age. If you are in any way worried about the menopause, visit your doctor.

Why do some women have regular periods while others have irregular periods?

Menstruation is a highly complex process involving many different hormones, the sex organs, other endocrine glands and the nervous system. Therefore it is not surprising that it doesn't run like clockwork for every women every month.

There are many factors which can upset this delicate balance.

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