Abstract
Endometrial receptivity is a crucial factor influencing implantation success in assisted reproductive technology (ART), although the ideal method for endometrial preparation for frozen embryo transfer (FET) is still disputed. Hormone replacement therapy (HRT) provides schedule flexibility and regulated hormonal management, whereas pure natural cycles (pNC) correspond with physiological hormonal patterns and may provide improved vascular adaptation. This study examines endometrial vascularity patterns and receptivity in HRT and pNC-FET protocols utilising two-dimensional (2D) power Doppler ultrasound, with the objective of establishing its diagnostic significance in guiding protocol selection.
A quantitative, prospective, descriptive, correlational design was employed, enrolling women undergoing FET at a fertility clinic in Abu Dhabi, United Arab Emirates. An endometrial assessment using 2D power Doppler ultrasound was conducted at the luteinising hormone (LH) surge during pNC cycles or on the corresponding progesterone initiation day in HRT cycles, and thereafter on the day of embryo transfer. Perfusion zones were categorised utilising the four-zone vascularity mapping technique, in conjunction with assessments of endometrial thickness and pattern. The success of biochemical implantation was assessed using serum beta-human chorionic gonadotropin (β-hCG) levels 10 days after embryo transfer. Statistical analysis was performed using SPSS Statistics 30.0, including descriptive statistics, chi-square tests and diagnostic performance metrics.
The results indicated that implantation rates were similar between the HRT (67.7%) and pNC (67.5%) groups. Nonetheless, vascular development from lower to higher perfusion zones occurred more frequently in pNC cycles, indicating enhanced responsiveness to an endogenous hormonal environment. In contrast, HRT cycles had a less varied vascular profile, with perfusion predominantly located in Zone II. The diagnostic assessment of 2D power Doppler ultrasound for predicting implantation demonstrated a sensitivity of 83.3% and a poor specificity of 13.0%, indicating that while favourable vascular patterns were often present in cycles that achieved implantation, they were also frequently observed in cycles that did not result in pregnancy.
The results underscore the value of 2D power Doppler ultrasound as an essential tool in evaluating endometrial receptivity, especially when combined with additional clinical and hormonal indicators. Although both HRT and pNC protocols can facilitate successful implantation, the vascular flexibility observed in pNC cycles may provide a benefit for certain individuals, particularly those with normal ovulatory activity. This study emphasises the significance of personalised protocol selection and supports the integration of Doppler-based vascular evaluation for a comprehensive FET planning approach.