GNRH1 and ovarian hyperstimulation syndrome: On the other hand, a significant lower Moderate-Severe OHSS rate was noticed when women were treated with GnRH antagonist protocols compared to those treated with the Long GnRH agonist protocol (9 studies; 1114 women; RR = 0.65, 95% CI: [0.52 to 0.82]; P = 0.0002; NNTB 15, NNTB 95% CI: [11 to 29]; I2 = 0%; χ2-P = 0.96; very-low quality evidence; Fig. 5).