RESUMEN
Summary: In order to compare GnRH agonist with antagonist protocol for the same patient during controlled ovarian stimulation cycles, the in vitro fertilization and embryo transfer (IVF-ET) outcome was retrospectively studied in 81 patients undergoing 105 agonist protocols and 88 antagonist protocols. The results showed that there was no statistically significant difference in duration of ovarian stimulation, number of ampoules, oocytes retrieved, serum estradiol (E2) and progesterone (P) levels,thickness of endometrium, the zygote-and blastocyst-developmcnt rate between GnRH agonist and antagonist protocols (P>0.05). High quality embryo rate was higher in antagonist protocols, but there was no significant difference between two protocols. Implantation rate and clinical pregnant rate were significantly higher in antagonist protocol (15.82% and 30.26%, respectively) than in agonist protocol (5.26% and 10.64% respectively (P<0.05). It was concluded GnRH antagonist protocol probably improved the outcome of pregnancy of older patients with a history of multiple failure of IVF-ET in a GnRH protocol.