Association between Available Blastocyst Formation Rate and Pregnancy Outcome Following Fresh Embryo Transfer

Abstract Background: Embryo quality usually has been regarded as a key predictor of successful implantation and pregnancy potential. The identification of embryos that have the capacity to implant and result in a healthy pregnancy is a crucial part of in vitro fertilization (IVF). Usually, the morphologically high quality embryos are chosen for embryo transfer in IVF treatment. The aim of this study was to assess the association between available blastocyst formation rate with pregnancy outcome following first fresh embryo transfer cycles. Our objective was to predict pregnancy outcome according to embryonic development potential, and provide a systematical individual treatment to adjust endometrial receptivity for the next transfer cycle. Methods: This retrospective, single-center study including 512 fresh embryo transfers conducted between 11/2019–08/2021, which consisted of 385 cleavage-stage (day 3) and 127 blastocyst-stage (day 5) transfers. The two groups were divided into clinical pregnancy group and non-clinical pregnancy group respectively for comparison. The association with available blastocyst formation rate and the clinical pregnancy rate between day 3 or day 5 transfer groups were concerned. Results: In the day 3 group, there were 275 clinical pregnancies, and the clinical pregnancy rate was 71.43%. Although the 2PN oocytes rate and available embryo rate at day 3 were significantly higher in clinical pregnancy group compared with non-clinical pregnancy group (P < 0.05), the blastocyst formation rate and the available blastocyst formation rate had no significant differences between the clinical pregnancy group and non-clinical pregnancy group (P > 0.05). In the day 5 group, there were 81 clinical pregnancies, and the clinical pregnancy rate was 63.78%. All the baseline characteristics had no obvious differences between the clinical pregnancy group and non-clinical pregnancy group (P > 0.05). The blastocyst formation rate in the non-clinical pregnancy group was higher than that in the clinical pregnancy group, but the difference was not statistically significant (81.06% vs. 77.03%, P = 0.083). Interestingly, the available blastocyst formation rate was significantly higher than the clinical pregnancy group (66.19% vs. 60.79%, P = 0.014). Conclusions: In fresh cycles, available blastocyst formation rate was not associated with pregnancy outcome with a day 3 embryo transfer. However, available blastocyst formation rate was negatively associated with pregnancy outcome with a day 5 embryo transfer.