What is the cause of ruptured ovarian cyst blood clots during period?

Normal: Each month, during an ovulatory cycle, one or more ovarian cysts are formed. One usually predominates and ruptures mid-cycle, liberating the egg. When the lining of the uterus is shed, bleeding occurs and clots form. If the uterus holds onto the clots, they will break down and the blood darken, resulting in a dark menstrual flow. If the uterus is irritable, the clots can be expelled as they form.