Transfer of mosaic embryos in ART practice: A systematic review and meta-analysis of clinical and neonatal outcomes

Introduction: Mosaic embryos have become a common finding following the advent of preimplantation genetic testing, sometimes constituting the only available option for transfer. However, clinicians remain uncertain as to whether they should be used. The study will examine clinical and neonatal outcomes of the transfer of such embryos. Methods: A systematic literature review and meta-analysis in four large databases was performed in accordance with established standards. The present study included clinical (clinical pregnancy rate, miscarriage rate, live birth rate etc) and neonatal outcomes (gestational age, birth weight etc). Results: Data from 22 eligible studies comparing euploid and mosaic embryos were included in the present analysis, encompassing 6170 mosaic and 34555 euploid embryos. Most studies were retrospective and utilized next generation sequencing. Clinical pregnancy, miscarriage and live birth rates for the transfer of mosaic embryos were 27-59%, 3-33% and 19-48% respectively. In most studied cases, mosaicism did not persist after implantation. Meta-analysis of comparative clinical outcomes indicated that mosaic embryos were inferior to euploid ones, with the exception of similar miscarriage rates and neonatal outcomes. Subgroup analyses indicated that low-level and segmental mosaic embryos had superior outcomes compared to high-level and whole chromosome mosaic embryos respectively, however, still performed more poorly compared to euploid embryos. Subgroup analyses based on study methodology, indicated that studies with next generation sequencing and those reporting live births instead of ongoing pregnancies, demonstrated similar performance of mosaic and euploid embryos for clinical outcomes, although these conclusions were based on a smaller number of transfers. Conclusion: Euploid embryos should constitute the priority for transfer, however, mosaic embryos, particularly low-level and segmental mosaic embryos ought not to be discarded and their transfer could be considered as an alternative to performing a new stimulation cycle in cases without any euploid embryos available.