Abstract
Background/Objectives: Accurate prediction of reproductive outcomes remains a key challenge in assisted reproductive technologies (ARTs). While embryo quality assessment has been extensively studied, endometrial receptivity has received less attention despite its critical role in implantation. Endometrial compaction (EC), i.e., the reduction in endometrial thickness between ovulation and embryo transfer, has been proposed as a potential predictor, but the current literature data is inconclusive. This study aimed to develop and validate a novel implantation predictor (IMP), based on extended assessment of endometrial shape and dynamics, which would be useful in determining reproductive success. Methods: The study analyzed data from 61 couples undergoing infertility treatment at the Kriobank Clinic (Białystok, Poland) between December 2021 and February 2025. Endometrial measurements were taken at the day following the ovulatory peak and on the day of embryo transfer. A set of normalized parameters describing endometrial dimensions was proposed and their changes over time measured. Based on the obtained data, a multivariable logistic regression model was constructed to create the IMP. Results: The proposed model demonstrated high predictive power for implantation, with an AUC of 0.839 (95% CI: 0.739-0.938). Statistically significant differences in IMP values were observed between the pregnancy and no-pregnancy groups (p < 0.0001). Quartile analysis showed that implantation rates increased from 6.25% in the lowest IMP range to 93.3% in the highest, confirming the model's strong predictive power. In the study group, the model is capable of predicting a quarter of cases in which implantation will almost certainly occur and another quarter in which implantation will almost certainly not occur. Conclusions: This study introduces a novel predictor (IMP) of implantation based on an extensive assessment of endometrial compaction, which may be used in predicting reproductive success. The findings show the importance of considering endometrial receptivity in ART success. They also indicate that integrating IMP with existing approaches may substantially improve predicting reproductive success.