Introduction: Endometrial blood flow reflects uterine receptivity. A study was done to look for a better predictor of endometrial receptivity with a novel 3D technique. Materials and Methods: Prospective cohort study was done on 203 women undergoing frozen embryo transfer (FET) cycles in a tertiary care center for a period of 2 years from November 2018 to November 2020 to see the correlation of endometrial and subendometrial blood flow assessed by 3D power Doppler. Various indices endometrial volume, subendometrial volume and their vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were obtained and compared between the pregnant and nonpregnant groups. The primary outcome was clinical pregnancy and ongoing pregnancy rates. Results: Out of 203 patients, 121 patients achieved pregnancy with a pregnancy rate of 59.6%. The endometrial and subendometrial volume was comparable between the two groups. Endometrial VI (3.3 ± 1.2 vs 2.8 ± 0.6; p < 0.01), FI (24.9 ± 3.0 vs 23.1 ± 2.7; p < 0.01) and VFI (1.4 ± 0.5 vs 1.1 ± 0.3; p < 0.01) were significantly higher in pregnant as compared to nonpregnant group. There was a significant difference in subendometrial VI (5.2 ±1.5 vs 4.4 ±1.9; p < 0.01), FI (26.0 ± 3.5 vs 25.0 ± 3.7; p = 0.04) and VFI (2.7 ± 1.1 vs 2.2 ± 0.6; p < 0.01) between two groups. Receiver operating characteristic (ROC) curves were plotted for these parameters and cut-off values were calculated. At the cut-off value of endometrial VFI of 1.18, gave sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 71.9%, 75.6%, 81.3%, 64.5%, and 73.4%, respectively while at the cut-off value of subendometrial VFI of 2.35, gave sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 66.9%, 63.4%, 72.9%, 56.5%, and 65.5%, respectively. A cut-off value of endometrial VFI of 1.18 and subendometrial VFI of 2.35, gave ongoing pregnancy rates of 67.3% and 59.5%, respectively. Conclusion: Endometrial and subendometrial vascularity by 3D power Doppler can be a useful novel parameter in predicting pregnancy in FET cycles.