A study analyzing the efficacy of GnRH-ant in presumed normal responders, i.e., IVF patients with a normal ovarian reserve, found a significantly lower risk of OHSS using the GnRH-ant protocol compared to the GnRH-a long-protocol was seen (21 RCTs; OR 0.69, 95% CI 0.57 to 0.83, n = 5,763; I2 = 15%) [91]. This evidence concerns the gene GNRH1 and ovarian hyperstimulation syndrome.