Data sub-analysis demonstrated no difference between the PPOS protocol and other specific protocol subgroups, except for the comparison with the GnRH-ant protocol in OHSS incidence (4 RCTs; RR 0.54, 95% CI 0.37 to 0.79, n = 901; I2 = 0%). This evidence concerns the gene GNRH1 and ovarian hyperstimulation syndrome.