The role of temporal changes in endometrial blood flow in natural and hormone replacement cycles with vitrified-warmed embryo transfer

Abstract

Background Uterine blood flow promotes endometrial development and subsequent implantation of fertilized eggs. We examined the temporal changes in uterine blood flow during natural and hormone replacement (HRT) cycles and clarified the relationship between uterine blood flow and assisted reproductive technology outcomes for vitrified-warmed embryo transfer (ET). Methods This was a retrospective cohort study. A total of 60 patients with vitrified-warmed ET were assigned to two groups according to the endometrial preparation: natural cycle (28 patients) or HRT cycle (32 patients). The uterine endometrial blood flow was evaluated using measurements of the radial artery resistance index (RA-RI) during the early follicular phase, the days of the human chorionic gonadotropin (hCG) trigger during a natural cycle or the start of progesterone administration during the HRT cycle, and the day of ET. We statistically and longitudinally measured and evaluated the RA-RI values of all individual patients. Results During natural cycles, the RA-RI on the day of ET was significantly higher than that during the early follicular phase. During HRT cycles, the RA-RI on the day of ET was also significantly increased compared to that during the early follicular phase. We validated the efficacy of the RA-RI values for predicting the possibility of pregnancy with vitrified-warmed ET. During natural cycles, the area under the receiver-operating characteristic curves (AUCs) for the early follicular phase, the day of hCG trigger, and the day of ET were 0.75 (95% confidence interval [CI], 0.57–0.93), 0.69 (95% CI, 0.49–0.88), and 0.60 (95% CI, 0.36–0.84), respectively. During HRT cycles, AUCs for the early follicular phase, the day of starting progesterone administration, and the day of ET were 0.60 (95% CI, 0.40–0.81), 0.60 (95% CI, 0.39–0.87), and 0.58 (95% CI, 0.37–0.79), respectively. Conclusions The uterine RA-RI increased at approximately the time of the implantation window compared to that of the early follicular phase during both natural and HRT cycles with vitrified-warmed ET. Our findings suggest that RA-RI during the early follicular phase might be effective and useful for deciding whether to choose the natural or HRT cycle for vitrified-warmed ET.