The aim of this study is to determine what is the best time interval between GnRH agonist (triptorelin acetate) ovulation induction allowing for the higher number of mature oocytes (MII) collected in IVF cycles.

Human chorionic gonadotrophin (hCG) has been the gold standard for ovulation induction for several decades. When GnRH antagonist protocols were introduced, it became possible to trigger final oocyte maturation and ovulation with a single bolus of a GnRH agonist (GnRHa) as an alternative to hCG. The use of GnRHa to trigger final oocyte maturation has potential advantages: the simultaneous induction of a FSH surge, higher numbers of mature oocytes retrieved as compared to hCG and the total elimination of ovarian hyperstimulation syndrome. From the earliest reports of GnRHa for ovulation triggering, it has been presumed that the timing of the ovum pick-up (OPU) after GnRHa administration should be the same as after hCG triggering (34-36 h). However, differences exist regarding the duration and profile of the GnRHa induced surge of gonadotrophins when compared with that of hCG. Even more, differences in the intra-follicular mechanisms involved in ovulation have been described after GnRHa and hCG trigger. No previous randomized controlled trials have been reported to evaluate the optimal interval of time between ovulation induction by GnRHa and oocyte collection. The present study compares the ovarian response and the IVF outcomes after induction by triptorelin 0.2 mg at four different time intervals: Group 1: OPU 24 hours after GnRHa administration. Group 2: OPU 30 hours after GnRHa administration. Group 3: OPU 40 hours after GnRHa administration. Group 4: control group: OPU 36 hours after GnRHa administration.