P-148 The importance of filopodia during early human embryonic development

Abstract

Abstract Study question The aim of this study was to examine the relation between the presence of filopodia and the embryo viability in human in vitro fertilised embryos. Summary answer The presence of filopodia related to a faster blastocyst development, a better blastocyst quality and higher morphokinetic scores which indicates a higher embryo viability. What is known already Filopodia are involved in numerous cellular processes, for example cell migration, neuronal extension growth and during embryonic development. There is no uniform name to describe these cytoplasmic string structures in the literature. Beside the frequent presence in different cell functions, we have limited information about its function in human embryos. In the early 2000s, the occurrence of filopodia or cytoplasmic strings at the blastocyst stage was classified as a negative sign of embryo viability, but more recently, it has been described as a positive feature, however, the importance and clinical significance of this structure is still controversial. Study design, size, duration Evaluation of the morphokinetic data on the development of 208 embryos from 78 IVF cycles. Examination was carried out at the Division of Assisted Reproduction, Department of Obstetrics and Gynaecology, Semmelweis University, Budapest between December 2020 and March 2021. Participants/materials, setting, methods Embryos from both conventional IVF (cIVF) and intracytoplasmic sperm injection (ICSI) treatments were analysed and evaluated. The dynamics of embryo development, embryo morphology and morphokinetic scores generated by time-lapse system was compared between the embryos with filopodia (FP+) and embryos without filopodia- (FP-) groups. Main results and the role of chance 81.2% of the embryos had filopodia in blastocyst stage. Embryos created by cIVF had 77%, while embryos fertilised by ICSI had 86% of filopodia presence (p = 0.08). FP+ embryos developed in a greater number into a higher quality blastocyst (52.1% vs 20.5%, p = 0,02), their KIDScore was higher (6.1 ± 2.1 vs 4,7 ± 2,07, p < 0.001) and they showed a tendency of higher implantation rate (39.7% vs 14.3% p = 0.16) than the FP- group. The dynamic of the early embryo development was similar between the two groups, however, FP+ embryos reached blastocyst stage significantly earlier (tB: 103.9 hours vs. tB: 107.6 hours; p = 0.007). Based on our results, there was a higher number of embryos with filopodia than without, and the presence of it is not related to the fertilisation method. These embryos developed faster into a blastocyst stage, their morphokinetic parameters were better. KIDScore and iDAScore embryo evaluation systems also recommend in a greater number the FP+ blastocysts for ET. We could also observe vesicle like transport along the filopodia, which leads us to believe that there might be a molecular communication between the differentiating cell populations. Limitations, reasons for caution Due to the low number of cases, the higher implantation rate is not significant. Wider implications of the findings The examination of this feature improves our knowledge of the early embryonic development and may help us to make decisions about the embryos with higher implantation potential. Trial registration number Not applicable