Aim: This study aimed to examine the relationship between the temporal changes in endometrial blood flow impedance during natural and hormone replacement therapy (HRT) cycles and clinical outcomes of vitrified-warmed embryo transfer (ET).
Methods: This retrospective observational cohort study included 60 women, 28 with natural, and 32 with HRT cycles, who underwent vitrified-warmed ET. Uterine radial artery resistance index (RA-RI) was measured during the natural and HRT cycles at the following time points: early follicular phase, day of the human chorionic gonadotropin injection during a natural cycle or day of progesterone administration during an HRT cycle, and day of ET.
Results: The clinical pregnancy rates of the natural and HRT cycles were 32.1% and 34.4%, respectively. The RA-RI at the early follicular phase was significantly lower in the pregnant group than in the nonpregnant group with natural but not HRT cycles (p = 0.04). The odds ratio for pregnancy was 0.70 (95% confidence interval [CI], 0.52-0.95) when the RA-RI value at the early follicular phase was increased by 0.01 in the natural cycle. With the natural cycle, the area under the receiver-operating characteristic curves for the RA-RI at the early follicular phase with a threshold of 0.68 was 0.75 (95% CI, 0.57-0.93), and the positive and negative predictive values were 0.53 (95% CI, 0.37-0.59) and 0.92 (0.74-0.99), respectively.
Conclusion: RA-RI at the early follicular phase might be an effective and useful tool for deciding between natural or HRT cycles for vitrified-warmed ET.
Keywords: endometrial blood flow; frozen embryo transfer; pregnancy; resistance index.
© 2020 Japan Society of Obstetrics and Gynecology.