Chocolate cysts do not shrink even after menstruation because they are caused by endometriosis. The foci of the ectopic disease are planted on the ovaries and bleed cyclically with menstruation, and the foci of the ectopic disease bleed during menstruation, so the chocolate cysts do not shrink even after menstruation has cleared. Chocolate cysts only gradually increase in size with each menstrual cycle, but do not shrink. Unless the endometrium stops bleeding after menopause, the chocolate cyst will not continue to increase in size, and surgery should be performed promptly.