The positions of the air bubble and the tip of catheter will be measured by transabdominal utrasonography among patients who have undergone high-quality frozen blastocyst transfer. The aim of this study is to compare pregnancy rates according to air bubble's final location in endometrial cavity. It is expected that the ET technique will be improved and live birth rates will increase by determining the optimal position of the embryo in the endometrial cavity during ET in patients who have achieved pregnancy.

Only patients who have high-quality blastocyst stage embryos will be included in the study. Since the implantation potential of high-quality embryos is high, possible embryo-induced implantation failure will be minimized. The positions of the air bubble and the catheter in the endometrial cavity in patients with and without pregnancy will be compared.

In patients participating in the study, the transfer catheter will be loaded using a "three drop technique," in which the drop of medium containing the embryo(s) is/are separated from a preceding and a following drop of the medium by an air bubble.

In hormonally prepared frozen embryo cycles, during embryo transfer in each patient, endometrial thickness, uterine cavity dimensions, distance of transfer catheter to the fundus, distance of released air bubble to the fundus, and distance of air bubble to side walls will be systematically measured and recorded under the guidance of transabdominal ultrasonography.

If the position of the embryo in the endometrial cavity is determined during ET in patients who have achieved pregnancy, an ET technique can be defined that predicts the optimum for the physician who will perform the transfer. Therefore, an increase in implantation and pregnancy rates can be achieved.

Inclusion Criteria:

• Exogenous hormone preparation of the endometrial lining
• High embryo quality ((≥2BB) according to Alpha criteria
• Embryo transfer at the blastocyst stage

Exclusion Criteria:

• Patients whose treatments were canceled for any reason before the embryo transfer procedure
• Patients who underwent embryo transfer in the cleavage stage
• Presence of low-quality (<2BB) blastocysts
• >15% loss of viability of the embryo during embryo thawing,
• Patients with congenital uterine malformations,

All patients who have artificial endometrial preparation with high-quality blastocysts between December 2021 and December 2022 will be included.