Not all women bleed every month. Elderly, post-menopausal women no longer have their periods. Pregnant women also stop having their menstrual cycles during pregnancy. In fact, if women miss their monthly period, it is a sign that they may be pregnant. Women have menstrual cycles because their body produces hormones to ready itself for pregnancy. A bunch of immature eggs from the ovaries will mature monthly but usually only 1 will remain alive and be ready to be fertilized. If fertilization occurs, then the egg will be implanted in the uterus, using tissues produced by the body and pregnancy will result. However, if a woman did not have sex or did not have her egg fertilized then the tissues that would have become the placenta will be discharged from the body. The discharge is what people see as blood. There is more than blood in the discharge. There is tissue and the unfertilized egg. Some women do experience menstrual pain, while others may become moody.