What is a period and why does it happen?
The first day of the menstrual cycle is the first day a woman has her period. A period is when the lining of the womb comes away
Periods usually lasts between 3 and 7 days
Periods are usually once a month and regular, but some women's periods are more unpredictable
Some methods of contraception can help make periods lighter, more regular, or allow women to control if and when they have a period (find out more)
It does no harm if contraception stops periods - there is no build up of blood inside, since the womb lining just stays thin (find out more)
After a period the lining of the womb begins to build up again
Period blood is not bad blood - period blood is darker because it comes out slower
How do women get pregnant?
An egg is released around the middle of the cycle (ovulation). The egg travels down the fallopian tube into the womb. If sperm fertilises an egg, it settles into the lining of the womb and an embryo begins to grow
The lining of the womb is needed to help the embryo grow, so the periods stop when a woman gets pregnant
If the egg isn’t fertilised by sperm, the lining of the womb breaks down and comes away (a period)
An egg is only available for fertilisation for 12 to 24 hours every month - that's one reason why women sometimes don't get pregnant straight away
Although an egg doesn't live long, sperm can live for up to a week - that's why women have to be so careful about unprotected sex