Going to the physiological understanding of trigger, the LH surge is something which develops last in the evolution of a girl from the irregular cycles and anovulatory menarche after three years of proper LH surge. Then, she becomes an ovulatory girl and this LH surge is different in different species.  In the animal kingdom like mating initiates a surge in rabbits and it’s a circadian rhythm in rats while it is a hypothalamic GnRH surge in sheep.  In the human LH surge and herein I would like to quote this paper by Mary Zeeman.  She says that ovulation, pregnancy all can occur without an accompanying GnRH surge.

The amplitude of LH surge or the rise of LH will decide the completion of the miosis, the first miotic division of the oocyte. The peak of an LH, amplitude the LH rise takes place that decides ovulation. So even 5% of LH rise is enough to complete the miotic process, but it would require an 85% LH rise to have actual ovulation to take place.  But then there is a certain duration of an LH surge so the LH surge plateaus for a period of about 14 hours. This completes the luteinization of all granulosa in the theca cells and converts them into lutein cells.  Then it confirms the adequacy of luteal phase progesterone levels while HCG in the circulation remains for a period of about 5 to 6 days and obviously there is no rise in LH, but HCG itself acts like an LH.  It is maintained continuous stimulation is maintained for a period of 5 to 6 days.  When the agonist is given, the LH rise is sharp and small.  In about four hours’ time, the correct amplitude of LH is reached but with next about 14 to 16 hours the LH reaches its top so the surge does not last beyond 20 to 24 hours.

The triptorelin and leuprolide whenever given as a trigger that would raise FSH value. Well, this FSH value will cause increased compactness of the cumulus cells. These cumulus cells are important because they are devoid of blood flow as they closes of the gap junctions. Due to compactness of the cumulus cells it will supply more nutrition to the oocyte and oocytes gets its last bit of thirst of the great nutrition, but that is very important.

A few other questions to be answered include:

• what is the impact of this recruitment profile on the follicles at the end of stimulation?
• What about follicle size at trigger?
• What should be an interval between HCG given the trigger of HCG and your ovum pickup?
• What about OHSS?
• What about HCG dose?

For detailed answers to these and other questions you might have on Deciding Trigger in IVF, enroll for live lectures by Dr. Sachin Kulkarni, MD, Chief Fertility Consultant – Sunanda IVF, Kolhapur, Runs Fellowship Program & Short Courses with Hands-On Training, Kolhapur, Published a paper- Influence of Diet in PCOS Phenotype in India in fertility sterility Aug 2019, here, https://docmode.org/deciding-trigger-in-ivf-dr-sachin-kulkarni/