When a woman bleeds from her vagina for a few days it is known as a period. A period occurs due to the changes in levels of the hormones oestrogen and progesterone. These hormones cause a thickening of the lining of the uterus. Once the lining is built up it is ready for a fertilised egg to attach and start developing. If there is no fertilised egg, the lining breaks down and bleeds resulting in a period.
 
Most women have a period every 28 days but this can range anywhere between 21 to 40 days. A woman’s period can last between 3 to 8 days with the heaviest bleeding in the first 2 days.  A woman will lose 5 to 12 teaspoons of blood during her period, although some may bleed more heavily than this.
 
Girls normally start experiencing a period by 12 years of age but it is normal for it to start earlier or later than this. In the first few years a girl’s period may not be regular.
 
Some women may experience period pains or cramps during this time. This occurs when the muscles in the uterus contract and relax to shed the built-up lining.