Abstract
The size and location of the corpus luteum and the presence of coexistent follicles are crucial factors in synchronizing recipients and determining the suitability for embryo transfer. However, there has been a recent decline in conception rates after embryo transfer, which is attributed to environmental pollution, uterine inflammation, ovarian cysts, and other factors. Therefore, we conducted experiments to establish a novel criterion for successful embryo transfer assessment. To assess the suitability for embryo transfer one day before transfer, we conducted ultrasound examinations equipped with a vaginal probe to evaluate the corpus luteum and coexistent follicle. We found that instances with corpus luteum and coexistent follicles (diameter: > 10 mm) constituted the majority (69.7%) of cases. When comparing the fertility rates of cases in which the corpus luteum and coexistent follicle (diameter: > 10 mm) were located on the same ovary and cases in which they were not, higher fertility rates were observed when the corpus luteum and coexistent follicle (diameter: > 10 mm) were on different ovaries. Our study revealed a high incidence of corpus luteum and coexistent follicles with a diameter exceeding 10 mm. Therefore, our findings suggest that the co-occurrence of the corpus luteum and a large follicle can serve as a new standard for the evaluation of embryo transfer suitability.