Optimizing frozen embryo transfer for low-quality embryos: Comparing outcomes in natural cycle and hormone therapy cycle - A retrospective analysis

Abstract

Objective: The aim of this study is to analyze potential disparities in clinical outcomes in two distinct regimens of frozen embryo transfer (FET): the natural cycle (NC-FET) and hormone therapy cycle (HT-FET), within the initial FET cycle of patients, according to embryo quality.

Materials and methods: A retrospective cohort study was conducted on 970 women who underwent a total of 1365 FET cycles at our hospital between January 2010 and October 2020. Excluding cases with missing data and multiple FET cycles, the final analysis included 670 women. Of these, 121 women underwent NC-FET, while 549 women received HT-FET after estrogen priming. The two groups were further stratified based on the quality of transferred embryos into a high-quality embryo group and a low-quality embryo group. Clinical outcomes including implantation rate, clinical pregnancy rate, live birth rate and miscarriage rate were compared using statistical analysis such as Pearson's Chi-square, Fisher's exact test, and Student's t-test. Logistic regression analysis was employed to estimate the adjusted odds ratio between NC-FET and HT-FET cycles, while accounting for potential risk factors.

Results: No statistically significant differences were observed in clinical outcomes between NC-FET and HT-FET. Subgroup analysis, after adjusting for age, number of transferred embryos, gravida, and parity, revealed no significant differences in clinical outcomes for patients with high-quality embryos. Patients transferred with high-quality embryos in HT-FET group exhibited a significantly higher implantation rate (45 %, 95 % CI: 0.41-0.50) than those in the NC-FET group (34 %, 95 % CI: 0.26-0.43; p = 0.034). On the other hand, patients transferred with low-quality embryos demonstrated a significantly higher live birth rate in the NC-FET group (adjusted odds ratio 2.57, 95 % CI 1.12-5.91).

Conclusion: Opting for NC-FET for low-quality embryos may yield a more favorable live birth rate compared to the HT-FET regimen.

Keywords: Frozen embryo transfer; HT-FET; Low-quality embryos; NC-FET; Poor-quality embryos.