Why do periods occur?
Females have small organs called ovaries in the lower part of their abdomen. The ovaries lie either side of the uterus (womb). The ovaries start to produce female hormones in girls around puberty which cause changes to the lining of the uterus (womb). Every month during your period the lining of the womb is shed together with some blood.
The time between the start of one period and the start of the next is called the menstrual cycle. The average length of a menstrual cycle is 28 days, but anything between 24 and 35 days is common. During the cycle various changes occur in the body. These are caused by changing amounts of the female hormones at different times of the cycle. The menstrual cycle is split roughly into two halves:
The first half of the cycle is called the follicular or proliferative phase. The levels of the two main female hormones, oestrogen and progesterone, are low to start with and you shed the inner lining of the uterus (endometrium). This causes a period (menstrual bleeding).
During this phase the ovaries are stimulated by hormones which are passed into the bloodstream from the pituitary gland (a gland near the brain). This causes some eggs in the ovaries to grow and mature in tiny fluid-filled cavities called follicles. The follicles produce oestrogen. Throughout the first half of the cycle the level of oestrogen in the bloodstream rises. One function of oestrogen is to cause the lining of the uterus to thicken (proliferate).
Ovulation occurs roughly half way through a cycle (about 14 days after the start of the period). This is when an egg is released into a Fallopian tube from a follicle in an ovary. The egg travels along the Fallopian tube into the uterus. The egg may be fertilised if you have recently had sex and there are sperm in the uterus.
The second half of the cycle is called the secretory or luteal phase. After ovulation, the follicle that released the egg makes a hormone called progesterone as well as oestrogen. Progesterone causes the lining of the uterus to swell, and be ready to receive a fertilised egg. If the egg is not fertilised, the levels of progesterone and oestrogen gradually fall. When they fall to a low level, they lose their effect on the uterus. The lining of the uterus is then shed (a period) and a new cycle then begins.
Normal periods (menstruation)
Starting to have periods is part of growing up for girls. Periods usually start to occur around the same time as other changes happen to the body, such as starting to develop breasts or to grow pubic hair. The average age to start periods is 13, but it is normal to start at any time between the ages of 11 and 15. A small number of girls may start before or after this. Periods continue until the menopause which is usually between the ages of 45 and 55.
What happens during a period?
For several days each month there is blood loss from the vagina. The amount of blood loss varies from period to period, and from woman to woman. Some women have a dark scanty loss, some have a heavier loss which is a brighter red. Sometimes clots are passed, especially if the loss is heavy. Sometimes there are small flaky fragments in with the menstrual blood. A normal amount of blood loss during each period is between 20 and 60 ml. (This is about 4 to 12 teaspoonfuls.) Bleeding can last up to eight days, but five days is the average. The bleeding is usually heaviest on the first two days. Some pain in the lower abdomen (period pain) is common and normal.
Do I have to avoid anything when I have a period?
No. Carry on as normal. If you find the periods painful then try to keep busy as this often helps. You can go swimming, have a bath, etc. Periods are not dirty; they are a normal part of a woman’s life.
Sanitary towels or tampons?
It is probably best to use sanitary towels when periods first start. These are placed in your underwear to soak up the blood. Tampons, which are towels that you insert into the vagina to absorb the blood, can be more convenient and can be tried later when you are more used to periods. They need to be changed regularly.
Other effects of the female hormones
The female hormones (oestrogen and progesterone) have other effects which you may notice apart from causing periods. For example, the texture of the mucus in the vagina changes at different times of the cycle. The vagina tends to be drier, and the mucus more thick, in the first half of the cycle. Shortly after ovulation, when progesterone levels rise, the vaginal mucus becomes thinner, more watery, and slippery. It becomes thicker again towards the next period as the progesterone level falls.
Progesterone may also cause water retention in various parts of the body. Your breasts may become slightly bigger or tender, and your abdomen may swell a little before a period. You may feel irritable before a period, which is possibly hormone-related. To have such symptoms before a period is normal. Sometimes the symptoms prior to periods can be more severe. This is then called premenstrual syndrome or premenstrual tension.
Some symptoms relating to periods
In general, if you have a change from your usual pattern that lasts for several periods, it may be abnormal. It is best to see a doctor if this occurs.
Heavy periods (menorrhagia)
This is common. It is difficult to measure blood loss accurately. Periods are considered heavy if they cause such things as: flooding, the need for double sanitary protection, soaking of bedclothes, passing clots, or if your normal lifestyle is restricted because of heavy bleeding. See your doctor if your periods change and become heavier than previously. There are various causes of heavy periods. However, in most women, the cause is unclear and there is no abnormality of the uterus or hormones. Treatment can reduce heavy periods, and is dealt with in more detail in a separate leaflet called ‘Heavy Periods (Menorrhagia)’.
Painful periods (dysmenorrhoea)
When periods first start they are usually painless. However, later on most girls notice an ache in their lower abdomen, back and tops of the legs, especially in the first few days of a period. The first two days are usually the worst. Some women have more pain than others. Painkillers or anti-inflammatory painkillers such as ibuprofen, usually ease the pain if it is troublesome. Another leaflet called ‘Period Pain’ gives details.
It is common to have some period pain. The cause of the pain in most women is not fully understood. Sometimes conditions such as endometriosis can make period pains become worse. See a doctor if:
- The pain becomes gradually worse each period.
- Pain begins a day or more before the onset of bleeding.
- Pain is severe over the whole time of the period.
Bleeding at abnormal times
If you have vaginal bleeding at times apart from your expected periods, you should see a doctor. This includes if bleeding occurs after you have sex, or after the menopause. There are various causes of bleeding between periods. One common cause is called breakthrough bleeding, which is small bleeds that occur in the first few months after starting the contraceptive pill. This usually settles over a few months.
Periods which stop (amenorrhoea)
Pregnancy is the most common reason for periods to stop. However, it is not uncommon to miss the odd period for no apparent reason. But, it is unusual to miss several periods unless you are pregnant. Apart from pregnancy, other causes of periods stopping include stress, losing weight, exercising too much (long-distance runners, etc), and hormone problems. As a rule, it is best to see a doctor if your periods stop for several months without explanation.
Also, see a doctor if your periods have not started at all by the age of 16.
The interval between periods can vary in some women. Irregular periods may indicate that you do not ovulate every month, and the balance of the female hormones may be upset. See a doctor if your periods become irregular in your younger years. However, irregular periods are common in the few years leading up to the menopause.
Further help and information
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