In IVF programmes, transvaginal ultrasonography is used as a non-invasive method to evaluate uterine receptivity. The aim of this study was to determine when to perform this investigation in order to optimize prediction of the likelihood of pregnancy. Over 9 months, 124 patients undergoing IVF or intracytoplasmic sperm injection were studied. The ultrasonographic evaluation included endometrial thickness, endometrial pattern, uterine artery pulsatility index, protodiastolic notch, end-diastolic blood flow, and endometrial-subendometrial blood flow distribution pattern. All patients underwent ultrasonographic investigation on the days of human chorionic gonadotrophin (HCG) administration, oocyte retrieval, and embryo transfer. Statistical analysis was done using recursive-partitioning analysis. The pregnancy and implantation rates per transfer were 33 and 19.8% respectively. In terms of single parameters, women with an end-diastolic blood flow, an endometrial-subendometrial blood flow and a multilayered endometrium were more likely to be pregnant than women without one or more of these signs. The most effective combination for evaluation of uterine receptivity was end-diastolic blood flow, endometrial pattern and endometrial thickness. Sensitivity and specificity of this combination were around 81%, positive predictive value was 68.2%, and negative predictive value 89.7%. The best sensitivity and specificity were obtained on the day of HCG administration: respectively 81.1 and 81.3%.