In the subgroup analysis for case–control study, a higher clinical pregnancy rate was observed in PCOS patients receiving GnRH-a pretreatment compared with the control group not receiving GnRH-a pretreatment (RR = 1.24, 95% CI: 1.11, 1.38, I2 = 60.4%). The gene discussed is GNRH1; the disease is polycystic ovary syndrome.