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.

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 drug that blocks the action of estrogens and so tricks the pituitary gland into thinking the ovary's follicles are not producing enough estradiol, so that natural FSH production is temporarily increased, the ovaries thereby are stimulated, and follicles grow. The LH surge and ovulation usually follow naturally, but human chorionic gonadotropin can be given if monitoring is used to make sure the follicle is properly mature. Brand names: Clomid (Marion Merrell) and Serophene (Serono)

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 GnRH-analog that briefly stimulates the pituitary gland to release follicle stimulating hormone (FSH) and luteinising hormone (LH), but then within a few days reduces these hormones to low levels (you could say that the pituitary has had a clamp put on it), stopping these hormones from competing with administered hormones -- and, particularly in women, suppressing the LH surge that otherwise can spoil the timing of egg retrieval in an assisted conception program such as IVF or GIFT. Examples include: leuprorelin(Lucrin, made by Abbott, used in Australia and Europe) or leuprolide (Lupron, made by Abbott in the US); nafarelin (Synarel, by Syntex); goserelin (Zoladex, by ICI); triptorelin (Decapeptyl, by Ipsen Biotech and used in Europe) and buserelin (Suprefact, by Hoechst, used in Europe).

Synonym for preovulatory follicle. A large, mature tertiary follicle that will respond to an adequate LH surge or injection of human chorionic gonadotropin (hCG) by undergoing ovulation, releasing its egg. Produces estradiol and, with exposure to LH or hCG, progesterone. Named after Reijnier de Graaf (1641-1673), the first person to see and to appreciate the importance of the ovarian follicle.

Part of the brain lying immediately above (and connected to) the pituitary gland; responsible for producing gonadotropin releasing hormone and dopamine, among other hormones and substances (including the endorphins, serotonin, etc.). In women (when conditioned to cyclical function by a lack of exposure to male sex hormones before birth) it resonates with the ovarian cycle and cooperates with the pituitary gland to cause corresponding cyclical production of follicle stimulating hormone and, particularly, a timely LH surge. Responds to progesterone by raising the body's temperature

(LUF) Occurs when a reasonably mature tertiary follicle (or preovulatory follicle) receives an LH surge that's enough to make it start producing progesterone, but is not enough to cause it to release its egg through ovulation. The result is that the egg is trapped in the follicle, which to a greater or lesser extent then functions like a corpus luteum, though this stage of the follicle's life is often shorter, giving rise to a luteal phase defect (LPD).

A large, mature tertiary follicle that will respond to an adequate LH surge or injection of human chorionic gonadotropin (hCG) by undergoing ovulation, releasing its egg. Produces estradiol and, with exposure to LH or hCG, progesterone.

Measurement of luteinising hormone in blood serum. Used in monitoring to judge the occurrence of the LH surge, if GnRH-analogs have not been employed. The result should be available within 4 hours of the test for this purpose.

Measurement of progesterone in serum. Often measured to check the occurrence of prior ovulation. Used to infer the onset of ovulation in ovulation induction or assisted conception programs, and attaches extra significance to an apparently raised serum LH in judging the onset of the LH surge during monitoring. The result should be available within 4 hours for these purposes. Abbr. serum P4.