GnRH agonist trigger fresh embryo transfers have similar outcomes but a lower dropout rate than freeze-all strategy: a retrospective analysis

Background: To compare pregnancy and delivery rate of the first fresh versus the first freeze all warming embryo transfer following a GnRH antagonist stimulation protocol with a GnRH agonist trigger. The secondary objective was to evaluate the dropout rate and the safety of the two approaches. Methods: A cohort retrospective study, set in a single university tertiary care fertility center. This study included all the first embryo transfers derived from oocyte retrievals performed between 01/01/2012 and 31/12/2020, following 1,396 GnRH antagonist induction cycles with GnRH agonist trigger. A total of 429 fresh (group A) and 967 warming embryo transfers (group B) were included. Results: The pregnancy and delivery rate resulted comparable in the two groups (Group A: 41.72%; Group B: 42.92%, p 0.678 and Group A: 35.43%; Group B: 33.20%, p 0.415, respectively). The only significant differences recorded were an increased miscarriage rate in Group B (p=0.008) and an increased multiple birth rate (p<0.001) and a lower dropout rate (p 0.010) in Group A. Conclusion: GnRH antagonist stimulation protocol with GnRH analogue trigger has been demonstrated to be an effective and safe technique. In addition, a subsequent fresh embryo transfer still represents a valid therapeutic option for physicians providing the desired outcomes in the first embryo transfer, with a lower dropout rate than the freeze-all strategy. ClinicalTrials.gov registration number: NCT05362734, retrospectively registered on 11 ^rd May 2022