Purpose : To identify embryo transfer position using two proposed new measurements in threedimensional (3D)/fourdimensional (4D) ultrasonography, and examine its relationship to pregnancy rate. Methods : We studied 105 cycles of in vitro fertilization and embryo transfer of good quality embryo performed between May and December 2016. Endometrial thickness and volume, distance from the embryo to the fundus (TDF), and as new measures, distance from the embryo to the center of both internal ostia

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... f the fallopian tubes (transfer distance of the lateral position [TDL]), and distance from the embryo to the central endometrium area (transfer distance of the front/back position [TDFB]) were measured. The pregnant and nonpregnant groups were compared. Results : The pregnancy rate was 23.8%. TDL values in the pregnant and nonpregnant groups were 26.9 ± 16.3 and 18.0 ± 16.0%, respectively, showing a significant difference (p= 0.011). There was a significant positive correlation between endometrial thickness and volume. Conclusions : The TDL was significantly longer in the pregnant group, implying the possibility that lateral deviation of the embryo transfer position does not affect the pregnancy rate. More accurate evaluation of embryo transfer site using 3D/4D ultrasound analysis may contribute to further improvement in pregnancy rates.