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
growing 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 grow
pubic hair. The average age to start periods is 13, but it is normal to
start anytime 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
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
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 'pre-menstrual syndrome' or 'pre-menstrual tension'.
Some symptoms relating to periods
In general, if you have a change from your usual pattern that lasts 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 another leaflet called 'Heavy Periods'.
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 'Painful Periods' 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 are 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.
Irregular periods
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
Women's Health Concern
Whitehall House, 41 Whitehall, London SW1A 2BY
Helpline: 0845 123 2319 Web: www.womens-health-concern.org
Provides advice to women on a wide variety of women's health issues including periods.
References
Menstrual cycle General Practice Notebook
Comprehensive patient resources are available at www.patient.co.uk
© EMIS and PiP 2008 Updated: 24 Jan 2008
