Assessing uterine receptivity in 2001: ultrasonographic glances at the new millennium

The understanding and control of embryo implantation represents the major challenge for assisted reproductive technologies. Along with developments in basic research and efforts to optimize embryo quality, the improvement of noninvasive and reliable methods to assess uterine receptivity constitutes an important step toward meeting such a challenge. Today, ultrasound-based approaches to evaluate endometrial echogenicity and uterine perfusion and contractility are available for practical use. Increasing evidence indicates that echogenic patterns of the endometrium reflect histologic processes that are involved in the establishment of receptivity. This constitutes a possible explanation for the reported association between premature hyperechogenic patterns of the endometrium and poor implantation rates. Nevertheless, additional studies aiming at correlating further morpho-biochemical events in the endometrium with its echogenicity patterns are needed. Further, developments in vascular assessment by Doppler, Doppler-related, and vascular detection technologies will also be instrumental in monitoring and improving vascular changes that lead to uterine receptivity. Finally, data supporting the hypothesis that uterine contractility, as visualized by ultrasound, influences in vitro fertilization-embryo transfer (IVF-ET) pregnancy rates encourage further investigation on both the regulation and control of uterine contractions. This article discusses some of the advantages and limitations of ultrasonographic assessments of uterine receptivity in the perspective of the new millennium.