P-194 Healthy babies after intrauterine transfer of mosaic blastocysts

Abstract Study question Can mosaic blastocysts be considered a valid alternative to patients undergoing IVF with no euploid embryos? Summary answer We believe that mosaic embryos can be a valid alternative when no euploid embryos are obtaines, particularly in diminished ovarian reserve and advance maternal age What is known already Preimplantational genetic screening is used to identify chromosomal euploid embryos and select them for intrauterine transfer in order to improve clinical IVF outcome.Chromosomal mosaicism is defined as two or more distinct chromosomical cells within an embryo and is a relatively common finding in human embryos. Mosaicism arises from mitotic errors occurring after fertilization or meiotic failures in gametes. The variables for the risk stratification of mosaic embryos have been defined as the percentage of mosaicism, specific chromosomes involved, monosomy versus trisomy and inclusion of complete or segmental chromosome mosaicism. High risk mosaic embryos may decrease implantation potential and increase miscarriages. Study design, size, duration A retrospective observational review of our results. During the period of 2017 - 2021 we performed 532 PGT-a studies. Embryos underwent blastocyst-stage preimplantation genetic testing for aneuploidy by next-generation sequencing. We obtained 39 low risk mosaic blastocysts, and from those we transferred 8 mosaic blastocysts. Participants/materials, setting, methods Patients in our clinic undergoing IVF treatment with PGT-a screening. Main results and the role of chance Our success pregnancy rate when transferring mosaic blastocysts was 62,5 %. From 10 mosaic embryos, 1 patient was lost in the study, 3 transferred embryos gave negative bHCG results and we obtained 5 ongoing pregnancies which resulted in 5 healthy babies. An amniocentesis was performed during the pregnancies to correlate the karyotype of the babies. The pregnancies were controlled with no pathological findings in detailed ultrasonography and the fetuses showed normal fetal growth. All pregnancies were delivered at term. Limitations, reasons for caution The main limitation of the study is the number of patients. A bigger size is needed in order to have full data which can support future decisions on whether to transfer mosaic embryos. Wider implications of the findings Our study shows that mosaic embryos can develop into healthy babies. Our study is small, but we have achieved a high pregnancy rate. Further studies should be performed in order to be able to counsel women who undergo PGAT-a screening in IVF cycles with only mosaic embryos. Trial registration number not aplicable