What changes are observed in the uterus if fertilisation does not occur?

In female, ovary produces one egg every month. The uterus also prepares itself to receive a fertilised egg. So, the wall of uterus becomes thick and soft containing lots of blood capillaries. If egg gets fertilised with sperm, then fertilised egg gets attached with uterus wall and gets nourishment from it. In case, egg is not fertilised, then the inner lining of uterus breaks down and comes out in the form of blood and mucus through the vagina. This cycle occurs every month and is called menstruation.