Before your first period

Reviewed by Dr Philip Owen, consultant obstetrician and gynaecologist

What are periods?
When girls become sexually mature and their bodies become capable of carrying a baby, they begin to produce female sex hormones. These are naturally occurring chemicals that control the development of breasts, the growth of pubic and armpit hair and also control periods.

Menstruation, or periods, are times when a girl or woman bleeds naturally from the vagina. Periods are a sign of health and show that the body is functioning as it should.

It is a good idea for a girl to talk to her mother about periods, or if this seems difficult or is not possible, she might prefer to speak to a sister, a cousin or someone else she feels comfortable talking to.

What happens in the body during a period?
The female reproductive organs inside a girl's body comprise:

the ovaries, which produce eggs and hormones.

the fallopian tubes, which connect the ovaries to the uterus.

the uterus (womb), a muscular organ where the egg can attach itself once it has been fertilized by a male sperm cell when pregnancy occurs.

the cervix or neck of the womb, which connects the uterus to the vagina.

the vagina starts at the bottom of the cervix and is the passage that leads outside the body. It does several things. It leads the blood out of the uterus and away from the body. The vagina is also the opening into which the man puts his penis during sexual intercourse and the channel through which a child is born.

When a girl reaches puberty, her hormones become active.

A hormone called oestrogen is made in the ovaries. Oestrogen affects the lining of the womb (endometrium) and makes it grow and develop.

After 10 to 14 days, the ovaries release an egg, and begin to produce another hormone called progesterone. The egg has now moved from the ovary to the uterus through the Fallopian tube. If the egg has not been fertilised by a sperm, the production of progesterone stops. When that happens, the lining of the womb comes away with a little blood and the girl gets her monthly period. The entire process takes about 28 days.

When do girls begin to have periods?
Most girls get their first period when they are 10 to 16 years old. The average age is 12.5 years. Women continue to have periods until they are 45 to 55 years old when the menopause occurs. Periods stop during pregnancy.

How often do women menstruate?
Periods happen about once a month. They last for four to seven days after which there is a pause of about 23 days (three weeks or so) until the next period, although the menstrual cycle varies from one girl to another. In some girls it may be longer or shorter than 28 days or it may be irregular, especially in the first few months after they have started.