A normal ovulatory cycle consists of follicular development, ovulation, corpus luteum development, and luteolysis. During the cycle, the endometrium undergoes proliferation, secretory change, and desquamation. This cycle is influenced first by the effects of estrogen alone, then by estrogen and progesterone, and culminates with estrogen and progesterone withdrawal. Progesterone stops the growth of the endometrium and stimulates its differentiation. In patients with anovulation, a corpus luteum is not formed, and the ovary does not secrete progesterone. Without progesterone, there is no desquamation or differentiation of the endometrium. Chronic unopposed estrogen causes continuous endometrial proliferation, and the endometrium becomes vascular and fragile, resulting in noncyclic menstrual bleeding. In addition, the endomet-rium may become hyperplastic and progress to a precancerous state, placing the patient at increased risk of endometrial cancer.6 See Table 49-1 for the pathophysiology of anovulatory bleeding relative to the specific conditions that contribute to it.
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