They are pharmaceutical analogues of GnRH hormone which suppress the premature surge of Luteinising Hormone (LH) that triggers ovulation. In this way, premature ovulation prior to oocyte retrieval is prevented. Prior to the use of GnRH analogues, there was a 20-30% cancellation rate of treatment cycles due to premature ovulation.
GnRH hormone is produced in the hypothalamus area and results in the production, storage and release of gonadotropin hormones FSH and LH from the pituitary gland. GnRH is released periodically (in waves) every one to three hours, depending on the phase of the cycle and is then followed by the release of the gonadotropins from the pituitary gland.
Why do we use GnRH analogues
It is well established that the rise and surge in LH results in the final oocyte maturation and ovulation. In IVF treatment we prefer to schedule ovulation at a specific time. A premature surge in LH would result in follicle rupture prior to egg collection and loss of the ovulated oocytes. The control of LH surge by its suppression is of great importance and has significantly reduced cycle cancellation. This control is achieved through the use of GnRH analogues.