The immature HPO axis.

One cause or anovulation may be an immature hypothalamic-pituitary-ovarian axis. The fact that initial menstrual cycles are usually irregular and often anovulatory implies that a maturation process is taking place in the HPO axis and that cyclic ovulatory menstruation begins only when adequate maturation occurs. Moreover, the external appearance of the ovary of a severely oligomenorrheic or amenorrheic female frequently is similar to that of a prepubertal female--this is, the ovary appears normal in size of slightly smaller, has a smooth, glistening surface without convolutions, and its capsule-like outer surface reveals few, if any, underlying follicles. A reasonable assumption is that there is inadequate gonadotropin stimulation of these ovaries possibly as a result of an immature HPO axis. The studies by radioimmunoassay of FSH and LH levels in prepubertal and pubertal females offer no statistical data by which to measure the maturity of the HPO axis, although consistently low FSH and LH levels may prove meaningful. Studies of FSH and LH in patients exhibiting gonadal dysgenesis neither support or disprove the immature HPO axis theory, but studies of idiopathic sexual precocity tend to support it. Studies using LH-RF in prepubertal and pubertal females indicate a pattern of response which may give useful information in the area.