A systematic review of 27 RCTs, conducted by Al-Inany in 2006 [2], showed that the clinical pregnancy rate was significantly lower with GnRH antagonist treatment than with the GnRH agonist long protocol, while the differences in the ongoing pregnancy and live birth rates did not significantly differ between the 2 groups; however, the incidence of severe OHSS was significantly lower in the GnRH antagonist group. This evidence concerns the gene GNRH1 and ovarian hyperstimulation syndrome.