Every month, new membrane linings form in the uterus to prepare for pregnancy. Then at a point usually halfway through your menstrual cycle, your ovaries release an egg, called an ovum. If this ovum becomes fertilised by a sperm, the mucous membrane remains. However, if there’s no fertilized egg, the uterus will begin to bleed approximately 14 days after ovulation. This bleeding is called a ‘period’, and it happens in order to rinse your body of the membranes, particles and fluids that have formed in the uterus. It usually happens for a few days, and then the cycle begins again. There are various stages to this process.