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Assessment of uterine receptivity prior to embryo transfer: a review of currently available imaging modalities.

This article aims to review in detail the current literature concerning the efficacy of, and problems associated with, the use of ultra-sonography and magnetic resonance imaging in predicting uterine receptivity and hence the outcome of assisted conception. Although the quality of the embryo and transportation to the uterine cavity are obvious requirements for in-vitro fertilization/embryo transfer treatment, attention has recently centred on the receptivity of the endometrium to the growing blastula. High resolution ultrasonography is currently the imaging modality of choice, but measurement of endometrial thickness is only associated with successful treatment outcome if ovarian stimulation includes clomiphene citrate. However, the ultrasonographic texture of the endometrium may have a greater prognostic value for implantation. The current literature is relatively unanimous that a 'triple' layered appearance of the uterus is associated with a 23-42% pregnancy rate and that endometrium is unreceptive when iso- or hyperechoic compared with myometrium. In an attempt to improve prediction rates, new techniques including magnetic resonance (MR) imaging are being used to determine uterine receptivity. Early results from MR imaging suggest that in patients treated with standard regimen of GnRHa, followed by human gonadotrophin (HMG), neither the endometrial thickness nor the volume is related to outcome. However, the relative signal intensity of the uterine layers provides good discrimination prior to embryo transfer, between pregnant and non-pregnant groups.