Anovulation; the inability of the ovaries to produce mature eggs or to release mature eggs on a regular basis. Among the most common causes of infertility in women, anovulation usually results from hormone imbalances, which may be caused by excessive weight loss, obesity, stress, or strenuous exercise. It also frequently occurs in women with polycystic ovarian syndrome (a Condition in which cysts develop in the ovaries). The most common cause of anovulation is excessive weight loss, which can result from the eating disorder anorexia bulimia or from excessive exercise. In many cases, treating the underlying cause and restoring the woman’s weight to normal is enough to restore fertility.