Premature luteinization (“premature LH surge”) occurs when prior to the planned initiation of the hCG trigger, a progressive rise in LH, irreversibly compromises follicle and egg development and maturation. It is not a sporadic isolated event. It comes as a culmination of a series ovarian events, occurring mostly in susceptible women (i.e. usually older women and those with diminished ovarian reserve. It is more likely to occur when the protocol used for ovarian stimulation has failed to maintain LH activity at a low level prior to and throughout the ovarian stimulation process.  Once it occurs in any given stimulation cycle it cannot be switched off by changing the stimulation in progress or by administering GnRH antagonists (e.g. Ganirelix/Cetrotide/Orgalutron) midway in the cycle in the hope that this could rescue the eggs under development. It is my opinion, once premature luteinization commences, the cycle is doomed and outcome is doomed to fail. The condition increases the likelihood of premature ovulation, failed release of eggs during needle-guided egg retrieval (so called “empty follicle syndrome” and the incidence of egg/embryo “incompetence” (chromosomal aneuploidy). This situation is most commonly seen in older women and in women who have severely diminished ovarian reserve.  In many cases its effect can be prevented through implementation of strategic and individualized protocols for controlled ovarian stimulation (COS) coupled with optimizing the type, timing and dosage of the “hCG trigger shot.”Normally, following optimal ovarian stimulation, the “trigger shot” is given for the purpose of it initiating meiosis (reproductive division) that is intended to halve the number of chromosomes from 46 to 23 within 32-36 hours. The hCG trigger also enables the egg to signal the “cumulus cells” that bind it firmly to the inner wall of the follicle (through enzymatic activity), to loosen or disperse, so that the egg can detach and readily be captured at egg retrieval (ER).Older women, and women with diminished ovarian reserve, tend to have more biologically active LH in circulation. LH causes production of male hormone (androgens, predominantly testosterone), by ovarian connective tissue (stroma/theca). A little testosterone is needed for optimal follicle development and for FSH-induced ovogenesis (egg development). Too much LH activity compromises the latter, and eggs so affected are far more likely to be aneuploid following meiosis.Women with the above mentioned conditions often have increased LH activity and are thus more likely to produce excessive ovarian testosterone. It follows that sustained, premature elevations in LH or premature luteinization (often referred to as a “premature LH surge”) will prejudice egg development. Such compromised eggs are much more likely to end up being complex aneuploid following the administration of the hCG trigger, leading to fruitless attempts at retrieval and the so called “empty follicle syndrome.”The developing eggs of women who have increased LH activity (older women, and women with diminished ovarian reserve) are inordinately vulnerable to the effects of protracted exposure to LH-induced ovarian testosterone. Because of this, the administration of medications that provoke further pituitary LH release (e.g., clomiphene and Letrozole), drugs that contain LH or hCG (e.g., Menopur), or protocols of ovarian stimulation that provoke increased exposure to the woman’s own pituitary LH (e.g., “flare-agonist protocols”) and the use of “late pituitary blockade” (antagonist) protocols can be prejudicial.The importance of individualizing COS protocol selection, precision with regard to the dosage and type of hCG trigger used, and the timing of its administration in such cases cannot be overstated. The ideal dosage of urinary-derived hCG (hCG-u) such as Novarel, Pregnyl and Profasi is 10,000U. When recombinant DNA-derived hCG (hCG-r) such as Ovidrel is used, the optimal dosage is 500mcg. A lower dosage of hCG or Ovidrel can, by compromising meiosis, increase the risk of egg aneuploidy, and thus of IVF outcome.