Comparison of uterine blood flow characteristics between spontaneous and stimulated cycles before embryo transfer

The Doppler blood flow characteristics of uterine arteries were evaluated prospectively in 57 patients undergoing embryo transfer. A total of 32 women underwent frozen-thawed (FT) embryo transfer during a spontaneous menstrual cycle (FT-embryo transfer), and 25 patients underwent in-vitro fertilization treatment (IVF-embryo transfer). The endometrial thickness, pulsatility index (PI), maximum peak systolic velocity (MPSV), minimum diastolic velocity (MDV) and flow velocity waveform type of the uterine artery blood flow were assessed with transvaginal colour Doppler ultrasonography before embryo transfer. The mean (SD) endometrial thickness was 9.2 (2.0) mm in FT-embryo transfer patients and 12 (3.4) mm in IVF-embryo transfer patients (P < 0.0003). There were no conception cycles in which the uterine arteries bilaterally had a flow velocity waveform with an absent end-diastolic flow. Compared to spontaneous cycles, the median PI was statistically lower and the MDV was higher in IVF cycles. In contrast, no difference was found in the median MPSV values between the two groups. There was no difference in Doppler velocimetry measurements between the conception and non-conception cycles in either the FT-embryo transfer or the IVF-embryo transfer groups. In conclusion, an inadequate uterine blood flow impaired implantation, while optimum uterine blood perfusion did not necessarily lead to conception.