Frequent blastocyst contractions with area reduction >30% are associated with reduced embryo quality but not IVF outcomes: A retrospective cohort study of fresh and frozen single embryo transfer

OBJECTIVE: This study aimed to analyze the effect of blastocyst contraction on embryo quality and subsequent in vitro fertilization (IVF) outcomes in women undergoing fresh single embryo transfer (SET) and frozen SET. MATERIAL AND METHODS: This retrospective cohort study included 300 patients who underwent 343 oocyte retrievals at Mackay Memorial Hospital between February 1, 2022, and February 29, 2024. The oocytes were divided into two categories based on whether blastocyst contraction occurred. We further analyzed the blastocyst morphology grading and KIDScore. We also analyzed subsequent fresh and frozen SET outcomes. Furthermore, we conducted a subgroup analysis for the frequency of contraction number and embryo quality. RESULTS: In all embryo analyses, the contraction group was associated with significantly lower morphology grading (good embryos 25.7% vs. 68.9%, fair embryos 27.4% vs. 4.3%, poor embryos 46.9% vs. 26.8%, p < 0.001) and lower KIDScore (≧8, 14.3% vs. 20.2%, ≧ 6 and < 8, 25.5% vs. 28.2%, <6, 60.1% vs. 51.6%, p = 0.020) compared to the non-contraction group. In the contraction number analysis, higher numbers (3-4 and ≧ 5 times) were associated with significantly poorer embryo quality than less numbers (1-2 times) (p < 0.001). However, in the fresh and frozen-thawed SET analyses, there were no significant differences in the clinical pregnancy, ongoing pregnancy, livebirth, and miscarriage rates between the contraction and non-contraction groups. CONCLUSION: The occurrence of blastocyst contractions-particularly at higher frequencies-was associated with poorer embryo quality. However, in the analysis of fresh and frozen-thawed SET, the clinical pregnancy, ongoing pregnancy, livebirth, and miscarriage rates were not significantly different between both groups, indicating that although contraction may reflect underlying differences in embryo viability, its impact on IVF success is minimal when high-quality embryos are selected rigorously for transfer. However, large research is needed to validate this conclusion.