A systematic review with meta-analysis, which included all RCTs comparing the efficacy and safety of GnRH-ant to the long-course GnRH-a protocol without restriction for the type of IVF population, demonstrated a significantly lower incidence of any grade of OHSS in GnRH-ant cycles compared to GnRH-a cycles (36 RCTs; OR 0.61, 95% C 0.51 to 0.72, n = 7,944; I2 = 31%) [83]. Here, GNRH1 is linked to ovarian hyperstimulation syndrome.