Many patients with polycystic ovary syndrome wonder why they can’t get pregnant when their menstrual cycles are regular and last 28 days each month. The key to pregnancy is not the regularity of the menstrual cycle, but the normal development of follicles. The small follicles on a woman’s ovaries grow gradually, and when they reach a diameter of 18mm or more, they are mature follicles. When the follicle matures and ruptures, the egg is discharged and the follicular cavity forms the corpus luteum, whose cells produce progesterone, also called progesterone. Estrogen in the ovary stimulates the growth of the endometrium, called the proliferative phase of the endometrium, and progesterone secretion stimulates the proliferative endometrium, which produces the secretory phase change, called the secretory endometrium. Progesterone is secreted through a 7-day period to its peak and then slowly declines through a 7-day period to its lowest point, luteal atrophy, when the lining begins to peel off and bleed, i.e., menstruation. Follicular development takes 14 days from the time it can be seen on ultrasound to the time the follicle matures, and 14 days from the time the corpus luteum forms after ovulation to the time progesterone is secreted to the time the corpus luteum atrophies, so a standard menstrual cycle is 28 days. Due to the difference in follicular development, it is normal for the menstrual cycle to start 7 days earlier or later. And there is a kind of menstruation for anovulatory menstruation. Patients do not grow large follicles, only small follicles, small follicles secretion of estrogen continues to stimulate endometrial hyperplasia, when suddenly a batch of small follicles atresia, resulting in a sharp decline in estrogen levels, it will cause estrogen withdrawal bleeding. In these patients, the endometrium has been stimulated by estrogen for a long time, and the endometrium is very thick. A sudden drop in the estrogen level will lead to a large amount of bleeding, which is why some patients say “like a hemorrhage” when they come to the doctor’s office. In other cases, the estrogen level is always very low, so there will be occasional bleeding. In both cases, there is no mature follicle development, no ovulation, and no corpus luteum to produce progesterone. Without progesterone stimulation, the uterine lining will not peel off, these bleeding are anovulatory bleeding. It can be seen that these “normal menstrual cycle” polycystic ovary syndrome patients, there is no mature follicle formation. Without ovulation, it is naturally impossible to get pregnant.