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

Research question: What is a suitable time interval between the last GnRH antagonist exposure and GnRH agonist (GnRHa) triggering for final follicular maturation? Design: 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. Results: 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). Conclusions: LH concentrations post-GnRHa trigger differ in regard to antagonist–agonist intervals, but the follicle/mature oocyte ratio achieved was not affected.