The impact of gonadotropin releasing hormone agonist (GnRH-a) on the quality and quantity of oocytes harvested in in vitro fertilization-embryo transfer (IVF-ET) patients was studied by comparing the results for patients stimulated with gonadotropin alone and with gonadotropin plus GnRH-a. Adding GnRH-a significantly improved the viable pregnancies per transfer and reduced the spontaneous abortions, which seemed to improve oocyte quality. However, when oocyte quality was evaluated by the fertilization rate and the implantation and delivery rates per embryos transferred, there were no significant difference in the results, indicating that GnRH-a did not improve the oocyte quality. On the other hand, GnRH-a significantly increased the average number of oocytes harvested, fertilized, and transferred, and this increased number of oocytes transferred has been demonstrated to increase pregnancy and multiple-pregnancy rates. Multiple pregnancy with more embryos implanted would significantly reduce the abortion rate. Abortion rates decreased inversely to the number of embryos implanted. Our data strongly suggest that the efficacy of GnRH-a on IVF-ET patients was due more to the quantity increase than the quality of embryos transferred.