P–249 Does the re-expansion of thawed embryos affect the clinical outcomes of human blastocyst vitrification?

Abstract

Abstract Study question Is that essential for prolonged culture of thawed blastocysts in order to be fully re-expanded before transferring? Summary answer Ongoing pregnancy rates decreased in blastocysts that not fully re-expanded after thawing. What is known already: The thaw survival of blastocysts is examined based on morphology of inner cell mass (ICM) and trophectoderm (TE). However, thawed blastocysts experience multiple changes in morphology and might be collapse after thawing due to the presence of blastocoel cavity. It is then difficult to evaluate blastocyst quality. Therefore, the blastocyst re-expansion is considered as a criteria to assess quickly the competent embryos. It also reflects the status energy metabolism from high quality embryo. After all, there are still some controversial opinions about the influence of re-expansion status after thawing. Study design, size, duration This was a retrospective study based on data collected between October 2019 and December 2020. A total 528 thawed blastocysts which were divided into two groups according to the post-thaw reexpansion status: fully re-expanded blastocysts (n = 416), partial or no re-expanded blastocysts (n = 112). The re-expansion status of blastocyst was assess prior to loading on the catheter by senior embryologists. Participants/materials, setting, methods Primary outcome is ongoing pregnancy. Only frozen single D5 transfer cycles were included. We excluded the frozen sperm/oocytes/embryos donation cycles, missing data, non-intact embryos after thawing. Statistical analyses were performed with T or chi-squared tests. Multivariable regression analysis was performed adjusting for the following confounding factors: age, BMI, embryo quality, re-expansion status, biopsied blastocyst. Main results and the role of chance Female age, BMI, number of previous cycles, endometrial thickness, positive HCG results, clinical pregnancy rate were comparable among patients within two groups. The rate of ongoing pregnancy rate in group 1 was significant higher compared with group 2 (51 vs 40.2, p < 0.05). The number of good quality blastocyst transferred in group 1 was higher than in group 2 (p < 0.001). However, under the same embryo quality, there were no difference between clinical pregnancy rate and ongoing pregnancy rate between two groups. When logistic regression were performed: only embryo quality, but not the re-expansion status, was noted to be an independent predictor of ongoing pregnancy (OR = 3.53;95% CI; 1.734–7.184;p=0.001). Limitations, reasons for caution The main limitation of the study is its retrospective design. Wider implications of the findings: Clinical outcomes are comparable between re-expanded blastocyst and partial or no re-expanded blastocysts, although ongoing pregnancy can be improved when embryos are fully expanded. As expected, blastocysts quality has the most important impact on ongoing pregnancy rate. Trial registration number Not applicable