To determine endometrial thickness, endometrial volumeand, endometrial and subendometrial blood flows, by using transvaginal two-dimensional (2D) and three-dimensional (3D) ultrasound examination and to compare the value of all the parameters in the prediction of endometrial receptivity during in vitro fertilization-embryo transfer (IVF-ET) cycles.

One hundred and twenty patients undergoing IVF cycles were recruited for this study. Transvaginal 2D and 3D ultrasound examination was performed to determine endometrial thickness, endometrial volume, pulsatility index (PI), resisitance index (RI) , systolic/diastolic ratio (S/D) of endometrial, subendometrial blood flows , vascularization index (VI), flow index (FI) and vascularization flow index (VFI) of endometrial and subendometrial regions by experienced sonographers on the day of human chorionic gonadotropin (HCG) injection. Statistical comparison was carried out by Mann-Whitney test. The receiver operator characteristic (ROC) curve analysis was applied and the area under the curve (AUC) was calculated. Statistic analyses were performed using SPSS 13.0. The two-tailed value of was considered statistically significant.

There were no significant differences between the pregnant group and non-pregnant group in endometrial thickness, endometrial volume (P>0.05). Patients in the pregnant group had lower PI, RI and S/D of endometrial and subendometrial blood flows than those in the non-pregnant group (Z=-3.811, -3.097, -2.071, P=0.001, 0.001, 0.038), with statisticalsignificant difference. Patients in the pregnant group had higher VI, FI and VFI of endometrial and subendometrial regions than those in the non-pregnant group (Z=-1.970, -2.698, -1.981, P=0.490, 0.007, 0.048; Z=-2.098, -2.090, -2.115, P=0.036, 0.037, 0.034), with statistical significant difference.

Endometrial and subendometria blood flows measured by transvaginal 2D and 3D ultrasound can be as a reliable indicator to assess endometrial receptivity and predict the pregnancy outcome. Among all the endometrial and subendometrial blood flow parameters, VI of endometrial and subendometrial are better predicators.