How far is too far? Does time interval between GnRH antagonist and GnRH agonist trigger in GnRH antagonist cycles matter?

What is a suitable time interval between the last GnRH antagonist exposure and GnRH agonist (GnRHa) triggering for final follicular maturation?A retrospective cohort study including 413 patients undergoing GnRH antagonist cycles in which GnRHa trigger was used, either solely or as a dual trigger. The primary outcome measure was the follicle/mature oocyte ratio. Cycles were analysed according to the time interval between the last GnRH antagonist exposure and the GnRHa triggering: Group 1 included patients with a 12-14 h interval; Group 2: 7-10 h interval; Group 3: 5-6 h interval and Group 4: 2-4 h interval. LH concentration was measured 11-13 h post-GnRHa injection.Median LH value was 65 IU/l. There was a weak but significant correlation between basal LH and the LH surge (R2 = 0.137, P < 0.001). Although square root LH values differed significantly between study groups (P < 0.001; higher in Groups 2 and 3), the follicle/mature oocyte ratio was not different across the four antagonist-agonist interval groups and no correlation was detected between the post-trigger LH concentration and the follicle/oocyte ratio (R2 = 0.011). In a model integrating age, day 3 FSH concentration, maximal oestradiol and body mass index along with the study groups, none of these factors was significantly related to the follicle/mature oocyte outcome ratio. Insufficient surge (LH < 15 IU/l) occurred in 14 (3.4%) cases. Rates of insufficient LH surge did not differ significantly between the groups (2.4%, 3.2%, 3.4% and 7.1% in Groups 1 to 4, respectively; P = 0.5).LH concentrations post-GnRHa trigger differ in regard to antagonist-agonist intervals, but the follicle/mature oocyte ratio achieved was not affected.