In PCOS patients [89], a reduction in the risk of OHSS was observed in those treated with GnRH-ant compared to those receiving a long-course GnRH-a protocol (9 RCTs; OR 0.65, 95% C 0.52 to 0.82, n = 1,114; I2 = 0%). This evidence concerns the gene GNRH1 and ovarian hyperstimulation syndrome.