Polycystic ovary syndrome often presents with menstrual irregularities and abnormal bleeding. Polycystic ovary syndrome refers to the ovaries having multiple small follicles developing, but without forming a dominant follicle, and hence no ovulation. Therefore, hormones often present as a single type of estrogen secretion, without the counteraction of progesterone after ovulation. Under the influence of estrogen, the endometrium gradually thickens. When it thickens to a certain extent, breakthrough bleeding occurs. Thus, the menstrual periods in polycystic ovary syndrome are often not normal menstrual flows but are breakthrough bleeding of the endometrium, generally irregular, and sometimes there may be significant vaginal bleeding.