Relationship between endometrial VFI values detected by three-dimensional power Doppler ultrasound and pregnancy outcomes in FET patients and prediction of the optimal VFI range-a retrospective cohort study.

BACKGROUND

The relationship between the vascular flow index (VFI) of the endometrium and the pregnancy outcome in the frozen embryo transfer (FET) cycle remains controversial, and there is currently no recommended optimal range for VFI.

OBJECTIVE

This study aimed to explore the relationship between three-dimensional energy Doppler ultrasound-detected VFI and pregnancy outcomes in FET patients and to determine the appropriate range of endometrial VFI.

METHODS

A retrospective analysis was conducted on the clinical data of 338 patients who received FET-assisted pregnancy treatment in the Reproductive Medicine Center of our hospital from January 2019 to January 2025. The patients were divided into four groups based on the quartiles of endometrial VFI values. The general data, three-dimensional energy Doppler ultrasound detection indicators, and pregnancy outcomes of the four groups were compared.

RESULTS

The abortion rates in Group 3 and Group 4 were significantly lower than those in Group 1 (p < 0.05). The multivariate logistic regression analysis showed that, compared with Group 1, the adjusted odds ratio (OR) values for Group 3 and Group 4 were 0.210 (95% CI 0.055-0.805) and 0.227 (95% CI 0.059-0.870), respectively, suggesting that the risk of abortion in the groups with high endometrial VFI values was significantly reduced (p < 0.05). The restricted cubic spline (RCS) analysis indicated a significant linear negative correlation between the endometrial VFI value and the abortion rate (p < 0.05), with a threshold of 0.1698045. This finding suggests that, after exceeding this threshold, the abortion rate decreases as the endometrial VFI value increases.

CONCLUSION

Three-dimensional energy Doppler ultrasound measurement of endometrial VFI values can be used as a predictive indicator for the risk of miscarriage in patients undergoing FET. When the VFI value is greater than 0.17, the pregnancy prognosis of the patients is better. During FET, clinicians can take a VFI of > 0.17 as an important reference index for evaluating endometrial receptivity and determining whether to perform embryo transfer.