This is the most common reason for abnormal bleeding and occurs commonly after puberty and before the menopause. As a result of non- ovulation, or improper function of the developing follicle or Corpus Luteum, one or both hormones which control the menstrual cycle i.e. Oestrogen and Progesterone, may not be secreted. This leads to a lack of support to the endometrium and irregular shedding and bleeding. It can also occur in reproductive years but is usually only temporary. Occasionally this occurs due to a functional ovarian cyst. Ultrasounds can help to identify which hormone is missing in order to rule out the possibility of a cyst and, so a course of treatment can be prescribed to correct the abnormality that cycle.