O-278 Prenatal outcomes of mosaic embryo transfer and neonatal assessment

Abstract

Abstract Ever-improving PGT-A methodologies now make it feasible to routinely detect chromosomal mosaicism. What is the appropriate clinical management of those embryos? What is the impact on pregnancies and births when such embryos are transferred? Mosaicism is the consequence of chromosome-segregation errors at mitosis, resulting in a mix of cells with different chromosomal content. The transfer of embryos with evidence of diploid-aneuploid mosaicism in their PGT-A results has become relatively common practice, and numerous clinics have published their experiences with such transfers. On average, ‘mosaic’ embryos have decreased potential to establish a pregnancy and higher risk for miscarriage compared to ‘euploid’ embryos, but pregnancies reaching term seem to produce apparently healthy babies. These findings favor an expansion of the binary ‘normal vs abnormal’ classification system of PGT-A to include ‘mosaicism’ as a third category. Further data suggest that features of mosaicism detected with PGT-A associate with different clinical outcomes, namely the mosaic level (percent aneuploid cells) and the mosaic type (nature of aneuploidy). ‘Low level’ mosaicism is preferable to ‘high level’ mosaicism, and segmental abnormalities are preferable to aneuploidies affecting whole chromosomes. Therefore, the ‘mosaic’ category can be further refined for optimal ranking purposes in the clinic. While many mosaic embryo transfers have resulted in babies, systematic and detailed follow-up studies on pregnancies from such embryos are urgently needed. The present talk will give an update on the ongoing data collection effort by an international, multicenter consortium containing 1700+ ‘mosaic’ embryo transfers, neonate information from 500+ babies born from those transfers, and 380+ associated prenatal test results. Analysis of the data reveals that late-term pregnancies and babies from ‘mosaic’ and ‘euploid’ embryos have largely equivalent health, with a few notable exceptions.