More is not always better–lower estradiol to mature oocyte ratio improved IVF outcomes

Aim: To find a cut-off ratio of estradiol/metaphase II oocyte (E2/M2) ratio and to evaluate the correlation with patients’ characteristics, embryo morphokinetics using EmbryoScope™ and IVF cycle outcomes. Material and methods: For this retrospective cohort study, records of all fresh cycles that were cultured and scored by EmbryoScope™ were evaluated. The peak E2/M2 ratio was calculated on the day of human chorionic gonadotropin (hCG) administration and correlated to embryo morphokinetic quality and cycle outcomes. A receiver operating characteristics analysis was calculated for the E2/M2 ratio and clinical pregnancy rates. Results: A total of 2461 oocytes were collected from 319 patients. Receiver operating characteristics analysis revealed a cutoff of 204 as a discriminative point to predict clinical pregnancy with a sensitivity of 69.5% and specificity of 62.1% (P < 0.001). E2/M2 > 204 group were older, had higher E2 concentration, fewer M2 oocytes despite elevated gonadotrophin doses. E2/M2 ratio ≤ 204 was correlated with higher fertilization rate, better embryo quality, higher pregnancy and live birth rates, and more frozen embryos. Conclusion: E2/M2 ratio < 204 yielded the best probability to achieve good quality embryos with good morphokinetic scores and better pregnancy outcomes and may be used to predict IVF cycle outcomes. Advanced maternal age and low ovarian response received higher concentrations of gonadotrophins, which resulted in higher E2/M2 ratio. Milder stimulation to those patients may improve their cycle outcomes.