GNRH1 and ovarian hyperstimulation syndrome: As shown in Table 1, compared to the GnRH agonist long protocol group, the GnRH antagonist protocol group had shorter duration of ovarian stimulation, lower peak estradiol level on the hCG trigger day and smaller number of fresh embryo transfer cycle cancellations due to OHSS risk (37.3 vs. 49.6%, [missing data, n = 1,263]), all with statistical significance.