Predictive factors influencing pregnancy rate in frozen embryo transfer

Purpose: To evaluate the outcomes of embryo transfer (ET) and to identify the parameters influencing pregnancy outcomes. Methods: This study included 938 ET cycles involving single frozen and thawed good-quality blastocyst (Gardner grade >/=3BB) between August 2017 and January 2018. The significance of several parameters including endometrial thickness, position of the transferred air bubble, self-evaluation score by physicians, and uterus direction at ET as predictors of clinical pregnancy was evaluated using univariate and multivariate analyses. Results: Among 938 ET cycles, 462 (49.3%) resulted in a clinical pregnancy. Endometrial thickness was positively associated with clinical pregnancy in a linear trend. Between the variable position of the transferred air bubble and clinical pregnancy rate showed a curvilinear relationship. Clinical pregnancy rate was higher in cases with good self-evaluation score, whereas there was no difference between groups with different uterus directions. Univariate analysis of predictive parameters identified endometrial thickness, self-evaluation score by physicians, and position of air bubbles as significant predictors of clinical pregnancy, of which endometrial thickness and position of air bubbles appeared to be independently related to clinical pregnancy. Conclusion: Endometrial thickness and the position of transferred air bubbles influenced clinical pregnancy in ET cycles.