Live birth rates in natural compared to artificial frozen blastocyst transfer cycles.

Abstract: Debate persists regarding the optimal endometrial preparation model for frozen embryo transfer (FET). Among the various approaches, the natural cycle and artificially programmed cycles are commonly employed. However, no established guidelines currently recommend a preferred method. The aim of the present study was to compare live birth rates after FET in natural cycle versus artificial cycle endometrial preparation in a non-selected, real-life population. This retrospective study included patients from a single centre who underwent vitrified-thawed blastocyst transfer between January 2016 and April 2023. In the natural cycle FET group, no medication was used, and the transfer date was determined by luteinising hormone ovulation test results. In the artificial cycle FET group, patients received oestradiol and progesterone tablets. A total of 905 cycles were analysed, which included 164 NC-FET cycles and 741 AC-FET cycles. From the 295 live births, there were a total of 320 neonates, with multiple gestations occurring in 8% of cases. The live birth rates were significantly higher in the NC-FET group at 43%, compared to 30% in the AC-FET group (P = 0.001). The AC-FET group also experienced higher rates of biochemical pregnancies and spontaneous abortions. However, when adjusting for confounding variables in multivariate analysis, the type of FET was not found to be an independent predictor of live birth.

Conclusion: Our findings suggest that while NC-FET is associated with higher live birth rates, other factors such as patient characteristics also play a significant role in these differences. Further prospective studies are needed to validate these results.