Factors affecting frozen embryo transfer success rates

Abstract Background This study aims to identify factors influencing the outcomes of frozen embryo transfer (FET) cycles. Methods A prospective observational study was conducted between July 2020 to December 2021 on 170 participants who underwent 190 FET cycles of autologous embryos after endometrial preparation with hormone therapy. Patient characteristics, ovarian stimulation details, and embryo specifics were recorded. Endometrial thickness, morphology, and Doppler flow were assessed on the day of progesterone start. Embryo details on the transfer day were also recorded. Serum ß-hCG levels were measured twelve days post-transfer, and those with levels > 25 IU/L underwent a 6-week ultrasound to detect a gestational sac. The clinical pregnancy rate (CPR) was calculated, and statistical differences between pregnant and non-pregnant groups were evaluated using Chi-square or Fisher’s exact tests for categorical variables and the Mann–Whitney U-test for continuous variables due to non-normal distribution. Logistic regression analysis was used to identify independent variables associated with successful pregnancy outcomes. Results For a total of 190 cycles, the CPR was 35.7%. Univariate logistic regression revealed that antral follicle count (AFC), Anti-Müllerian hormone (AMH), blastocyst transfer, embryo quality, blastocyst quality and transferring more than one embryo (double or triple) were significantly associated with CPR. On multivariate analysis, embryo quality remained the only independent predictor of successful FET outcomes. Conclusion Embryo quality is the strongest predictor of FET success, with significant effects seen for good-quality embryos, blastocyst transfers, and the number of embryos transferred. Age and ovarian reserve also influenced outcomes. Endometrial factors showed only trends, warranting further investigation. Tailored treatment approaches are crucial for optimising IVF success.