The Influence of Estradiol/follicle and Estradiol/oocyte Ratios on the Outcome of Controlled Ovarian Stimulation for in Vitro Fertilization

Objective: The aim of the study was to evaluate the influence of the ratios of estradiol (E2) to either the number of follicles >14 mm on the day of human chorionic gonadotropin administration (E2/follicle) or the number of oocytes retrieved (E2/oocytes) during controlled ovarian hyperstimulation (COH) with gonadotropin-releasing hormone (GnRH)-agonist (agonist group) and GnRH-antagonist (antagonist group), on the outcome of in vitro fertilization (IVF) cycles.

Patients And Methods: All consecutive women aged <35 years admitted to our IVF unit during a 6-year period with normal to high response to COH were retrospectively studied. Ovarian stimulation characteristics, number of oocytes retrieved, number of embryos transferred and pregnancy rate were assessed.

Results: Six hundred and ninety consecutive IVF cycles were evaluated, 301 in the agonist group and 389 in the antagonist group. The ratios of E2/follicle and E2/oocyte were significantly higher in the agonist group (p < 0.001 for both). Moreover, while pregnancy rates within E2/oocyte ratio of 100-200 pg/ml were comparable between the agonist and antagonist groups, when E2/oocyte ratios were <100 pg/ml or >200 pg/ml, pregnancy rates were significantly higher in the agonist group. Furthermore, no difference in pregnancy rates was observed within the agonist group between different E2/oocytes ratios, while within the antagonist group, higher pregnancy rates were observed when comparing those with E2/oocyte ratio of 100-200 pg/ml with those with E2/oocyte ratio <100 pg/ml or >200 pg/ml.

Conclusion: While E2/oocyte ratio cannot predict the success of GnRH-agonist protocol, patients undergoing GnRH-antagonist protocol should reach E2/oocyte ratio within the 100-200 pg/ml range in order to achieve the best IVF outcome.