A GnRH-analog that (unlike GnRH-agonists) immediately stops the pituitary gland from releasing the gonadotropins follicle stimulating hormone (FSH) and luteinising hormone (LH). Can substitute for GnRH-agonists for many gynecological purposes (particularly to suppress the LH-surge in assisted conception), although its use with pure FSH preparations (such as Fertinex, Gonal-F, Metrodin HP or Puregon) can lead to poor egg quality unless the dosage is carefully controlled or some luteinising hormone is added to the stimulation regimen.

The GnRH-antagonist ganirelix made by Organon. Called Orgalutran outside the US.

A GnRH-antagonist made by Serono. Approved for women undergoing in vitro fertilisation), with good results when started on day 7 of the cycle, after 5 or 6 days' Gonal-F in suppressing the LH surge; the dosage, however, appears to be critical, to avoid over-suppressing natural luteinising hormone. Marketed as Cetrotide.

A GnRH-antagonist made by Organon. The first to be FDA approved for women undergoing in vitro fertilisation), with good results when started on day 7 of the cycle, after 5 or 6 days FSH in suppressing the LH surge; the dosage, however, appears to be critical, to avoid over-suppressing natural luteinising hormone. Marketed as Antagon in the US and as Orgalutran elsewhere.

A sudden and huge increase in production of luteinising hormone by the pituitary gland in response to sustained and substantial levels of estradiol in the blood in women, midway through the ovarian cycle. Causes ovulation about 36 hours after it starts (about 20 hours after its peak). If not suppressed during assisted conception (see GnRH-agonists and GnRH-antagonists) it can start before human chorionic gonadotropin has been given, so spoiling the timing of egg retrieval. Timely production of the LH surge in adult women depends on female conditioning of the hypothalamus and/or the pituitary gland before birth. Detectable by testing the urine with a special kit.

(LH) The hormone, or gonadotropin, produced by the pituitary gland to cause, in women, ovulation of a mature follicle in the ovary, resulting in formation of the corpus luteum; in men, stimulates the production of testosterone by the Leydig cells of the testis. Suppressed by GnRH-agonists and GnRH-antagonists, so that (for ovulation induction) an injection of human chorionic gonadotropin (hCG), which acts the same way, has a predictable time course of action. A small amount of LH is essential for normal function of the tertiary follicle and the corpus luteum. Recombinant LH is under development by Serono as Luveris, but its clinical role in place of hCG is not yet established.

The GnRH-antagonist ganirelix made by Organon. Called Antagon in the US.