No evidence of a significant difference was found between the r-LH supplementation group and the r-FSH alone group regarding incidence of ovarian hyperstimulation syndrome (OHSS) (three trials: OR 0.84, 95% CI 0.25 to 2.78) , r-FSH total dose used per treatment cycle (two trials: WMD -211.90, 95% CI -319.99 to -103.82), serum oestrodial level on hCG day (WMD 321.71, 95% CI -117.44 to 760.86), number of retrieved oocytes per oocyte retrieval (two trials: WMD -0.69, 95% CI -1.52 to 0.13), r-FSH total dose used per treatment cycle (two trials: WMD -211.90, 95% CI -319.99 to -103.82). This evidence concerns the gene PLOD1 and ovarian hyperstimulation syndrome.