RETROSPECTIVE ANALYSIS OF 479 PGT-SR CYCLES - ANALYSIS OF CHROMOSOME INFORMATION AND AVAILABILITY OF EMBRYOS FOR TRANSFER

Abstract

Analysis of data from 479 PGT-SR cycles, to investigate the impact of the type of rearrangement, gender of carrier, day of biopsy and maternal age. To use this data to provide a set of practical guidelines for genetic counsellors to advise patients on their likelihood of having embryos available for transfer. Inter-chromosomal effect and uniparental disomy were also investigated. Data was collected on 1814 trophectoderm samples submitted for PGT-SR via NGS over a 5yr period, 2015-2020. Embryos were classed according to the chromosomes involved in the rearrangement – balanced/unbalanced – and according to the status of the chromosomes not involved in the rearrangement – euploid/aneuploid/mosaic. Analysis was undertaken to compare the data generated by the different types of structural chromosome rearrangement. For each separate indication, data was then analysed according to the sex of the carrier, maternal age, and day of biopsy. The proportion of incidental aneuploidy – aneuploidy in chromosomes not involved in the rearrangement – and mosaicism was examined by rearrangement type for evidence of inter chromosomal effect. The number of cycles with at least one embryo available for transfer was also calculated in each group and sub-group. The two-tailed Fishers exact test was used for statistical analysis comparing reciprocal translocation, Robertsonian translocation and inversion cycles. Data was also collected on other indications, but numbers were too low for statistical analysis. The proportion of Euploid/Balanced samples for reciprocal translocations was significantly lower than the Robertsonian group (P<0.0001) and inversion group (p=0.0219). An increased rate of incidental aneuploidy was observed in the inversion group, which correlated with a higher average and median maternal age. The Robertsonian group had a significantly higher chance than the reciprocal group of having at least one embryo available for transfer (p=0.0225). The sex of the carrier of the rearrangement only impacted the Robertsonian group, producing more unbalanced embryos from maternal carriers, but not impacting the overall proportion of cycles with embryos available for transfer. Increasing maternal age increased the rate of incidental aneuploidy and reduced the proportion of cycles with embryos for transfer across all groups. It also appeared to increase the proportion of unbalanced embryos in the Robertsonian group. Day of biopsy did not appear to impact on cycles. No evidence was observed to support interchromosomal effect and no uniparental disomy was observed in samples tested. The factors investigated altered the proportions of different cytogenetic constitutions, but not the availability of embryos for transfer, with the exception of maternal age. PGT-SR cycles for Robertsonian translocations and inversions have the highest chance of identifying embryos for transfer.