Failure of positive feedback.

Failure of the hypothalamic-pituitary unit to release LH in response to oestrogen may be encountered with or without associated disturbance of negative feedback. Such positive feedback failures can be detected with the aid of an oestrogen provocation test. Application of this test in women presenting with anovulatory cycles permits one to distinguish between an hypothalamic or ovarian cause (e.g. deficient follicular development) for anovulation. In women with infrequent or absent menstruation and infertility an oestrogen provocation test, combined with basal gonadotrophin and prolactin measurement and pituitary response to LH-RH, may prove to be useful in selecting the appropriate treatment for induction of ovulation.