Using 2D/3D ultrasound observation of endometrial thickness, endometrial volume, and blood flow changes to predict the outcome of frozen embryo transfer cycles: a prospective study

Background: Endometrial thickness (EMT) and blood flow are commonly used indicators of endometrial receptivity. However, the results of single ultrasound examination studies differ. Therefore, we used 3-dimensional (3D) ultrasound to study the influence of changes in EMT, endometrial volume, and endometrial blood flow on frozen embryo transfer cycles. Methods: This was a prospective cross-sectional study. Women who underwent in vitro fertilization (IVF) at Dalian Women and Children's Medical Group and met the inclusion criteria were enrolled between September 2020 and July 2021. Ultrasound examinations were performed in patients who underwent frozen embryo transfer cycles on the day of progesterone administration, the third day after progesterone administration, and the day of embryo transplantation. Two-dimensional ultrasound was used to record EMT, 3D ultrasound was used to record endometrial volume, and 3D power Doppler ultrasound imaging was used to record the following endometrial blood flow parameters: vascular index, flow index, and vascular flow index. Changes in the 3 inspections of the EMT, volume, vascular index, flow index, and vascular flow index and 2 inspections of estrogen levels were categorized as "declining" or "nondeclining". The relationship between changes in a certain indicator and the IVF outcome was analyzed by univariate analysis and multifactorial stepwise logistic regression. Results: In total, 133 patients were enrolled in this study, 48 were excluded, and 85 were included in the statistical analysis. Among these 85 patients, 61 were pregnant (71%), 47 had a clinical pregnancy (55%), and 39 had an ongoing pregnancy (45%). The results showed that if the first change in endometrial volume was nondeclining, the outcomes of clinical and ongoing pregnancies were more likely to be unfavorable (P=0.03, P=0.01). Additionally, if the second change in endometrial volume on the day of embryo transplantation was nondeclining, the outcome of an ongoing pregnancy was more likely to be favorable (P=0.03). Conclusions: The changes in endometrial volume was a factor helpful in predicting the IVF outcome, whereas the changes in EMT and endometrial blood flow analyses were not helpful in predicting IVF outcome.