The incidence rate of moderate and severe OHSS was remarkably lower in the GnRH-a group and GnRH-a + 1000 IU hCG groups than in the GnRH-a + 2000 IU hCG and GnRH-a + 3000 IU hCG groups; no significant difference was noted between the GnRH-a group and GnRH-a + 1000 IU hCG groups and between the GnRH-a + 2000 IU hCG and GnRH-a + 3000 IU hCG groups (p < 0.05, Table 2). This evidence concerns the gene GNRH1 and ovarian hyperstimulation syndrome.