In a flexible antagonist protocol, earlier, criteria-based initiation of GnRH antagonist is associated with increased pregnancy rates in IVF.

Background: The purpose of the study was to assess ongoing pregnancy rates across groups of patients treated by IVF, which were defined according to criteria aimed at the prevention of premature LH surge and used for initiating GnRH antagonist.

Methods: This is a prospective observational cohort study. During the last 3 years, in IVF-ICSI patients undergoing controlled ovarian stimulation (COS) with the antagonist protocol, the antagonist administration was initiated according to at least one of the following patient-specific criteria: (i) at least one follicle measuring >14 mm; (ii) estradiol levels >600 pg/ml; and (iii) LH levels >10 IU/l.