This is a clinical term used to describe abnormal uterine bleeding not attributable to a pathologic lesion of the endometrium or uterus. The cause is usually due to ovarian dysfunction, which may result in anovulation or in luteal phase defect.
Anovulation can occur at any age but more commonly occurs at menarche and at menopause.
In an anovulatory cycle, the failure of ovulation leads to excessive and prolonged estrogen stimulation, with absence of the postovulatory surge in progesterone levels. This results in a disordered proliferative endometrium. The spiral arterioles do not develop properly in the absence of progesterone. In some cases, there is no drop in estrogen levels and bleeding occurs because adequate blood supply to the proliferating endometrium cannot be maintained. The exact cause of anovulation is not really understood.