Fertility 2025

Valerie and Karen are part of a mainstream PGT group that support patients with genetic information counselling for mosaic embryos. At Fertility 2025 the group discussion was shared to highlight the dilemmas and consensus for counselling patients considering transfer of PGT-A embryos reported as mosaic. 

 

The abstract included in Fertility 2025 publications and is shared below. 

Authors: Valerie Shaikly, Karen Sage, Sara Levene, Jennifer Sloane, Claire Engelbrecht, Elizabeth Verdon, Alyssa Armsby 

 

The experience and views of seven UK specialist genetic counsellors supporting patients considering transfer of putative mosaic embryos was sought. The most prominent theme was challenges patients face managing uncertainty confronting a potential genetic finding with unknown clinical impact; compounded by the variability in reporting and interpretation of mosaic results provided by laboratories using different technology platforms. 

Consensus for the relevance of high or low level mosaic findings was unclear due to clinic requests to mask mosaic reporting, non-standardised allocation of mosaic call levels between laboratories, and the utility attributing a level for a sample of unknown size (approximately 4-8 trophectoderm cells). Embryos reported as low or high mosaic for chromosomes 13, 18, 21, X and Y could be considered for transfer with personalised genetic counselling, and recommendations for prenatal testing. 

Prenatal testing advice favoured amniocentesis as the preferred option due to lack of NIPT validation across 24 chromosomes. While CVS could provide reassurance, the inability to detect the occurrence of CPM was noted. The group reflected that few patients sought testing for chromosome balance for PGT pregnancies and difficulty obtaining follow up data from patients undergoing prenatal testing, as this does not take place in fertility clinics. 

Also addressed was the current evidence on follow up studies of mosaicism persisting in ongoing pregnancies given as 1.2%; PGT-A error rate is cited at ~1-2% potentially equating an anxiety risk equivalent to transferring a euploid embryo. 

Members were re-assured in their practice and welcomed continued dialogue as new evidence becomes available in this field.