Three-Dimensional ultrasound parameters in assessing endometrial receptivity: a prospective study of novel scoring systems in frozen embryo transfer cycles

Accurate prediction of endometrial receptivity remains a key challenge in assisted reproductive technology (ART), with implantation failure often attributed to suboptimal endometrial conditions. This prospective observational study was conducted at the Department of Reproductive Medicine & Surgery, Kasturba Hospital, Manipal, between September 2024 and June 2025, to develop novel ultrasound-based scoring systems for predicting clinical pregnancy in frozen embryo transfer (FET) cycles. A total of 256 women aged 21–50 years undergoing FET with embryo(s) derived using their own gametes in natural, stimulated, or hormone replacement cycles were recruited, provided they had at least one good-quality embryo transferred. Patients with Müllerian anomalies or acquired intrauterine pathologies were excluded. Endometrial parameters including thickness, echogenicity, vascularity, peristalsis, uterine artery pulsatility index and 3D endometrial volume were evaluated on the day of FET using standardised ultrasonography. The primary outcome was clinical pregnancy, confirmed by visualisation of a gestational sac at six weeks. The study was registered with the Clinical Trials Registry–India (CTRI/2024/10/075117). The trial was approved on 11/10/2024. Of the 256 FETs, 103 resulted in clinical pregnancy (40.23%). Women who conceived had significantly greater endometrial volume (median 4.40 vs 3.60 mm³; p < 0.01), higher vascularity (74.8% vs 62.1%; p = 0.0417), and lower peristalsis (2 vs 3 waves/min; p = 0.0231) than those who did not conceive. Male factor infertility was more frequent in the pregnant than in the non-pregnant cohort (32.03% vs 10.45%; p < 0.01). Logistic regression confirmed endometrial volume, vascularity, and reduced peristalsis as independent predictors of pregnancy (p < 0.05). Three scoring systems were developed: the Total Screening Score (all predictors), the Targeted Endometrial Receptivity Score (volume, vascularity, peristalsis), and the Endometrial Volume Score. The Total Screening Score (≥14) offered the highest specificity (0.712) but poor sensitivity (0.097) and overall accuracy (0.464). The Targeted Score (≥7) achieved balanced performance, with sensitivity 0.631, specificity 0.621, accuracy 0.625, and the highest positive likelihood ratio (1.665). The Endometrial Volume Score (≥2) demonstrated the best sensitivity (0.796) and negative predictive value (0.727), serving as a strong screening tool, though limited by low specificity (0.366). This study introduces the first multiparametric ultrasound-based scoring framework for FET outcomes developed in the Indian context. The Targeted Endometrial Receptivity Score provides a balanced, reproducible tool for FET planning and patient counselling, while endometrial volume alone can serve as a rapid screening parameter. These systems offer a cost-effective, non-invasive approach to optimise FET outcomes, though validation in larger, multicentre cohorts is warranted.