P-235 Impact of repeated vitrification and biopsy on clinical outcomes: a comparative study of once-frozen and thaw-biopsy-refreeze embryos

Abstract

Study question Does the transfer of thaw-biopsy-refreeze embryos have different clinical outcomes than the transfer of biopsied once-frozen embryos? Summary answer There were no significant differences in clinical outcomes (implantation, clinical pregnancy, live birth rates) between once-frozen and TBR embryos. What is known already Genetic testing of previously unbiopsied frozen embryos through “thaw, biopsy, refreeze” (TBR) has become common as pre-implantation genetic testing for aneuploidy (PGT-A) has become mainstream. However, it remains uncertain whether embryos undergoing multiple vitrification cycles exhibit diminished pregnancy outcomes due to potential damage from repeated freezing and thawing. This study aimed to compare clinical outcomes between once-frozen and TBR (twice-frozen) embryos. Additionally, we investigated whether once-biopsied and twice-biopsied TBR embryos differed in their clinical outcomes. Study design, size, duration This retrospective, single-centre cohort study included 421 embryos from patients undergoing assisted reproductive technology (ART) treatment: 374 once-frozen embryo transfers were performed in 305 patients. 47 TBR embryo transfers in 44 patients, of which 36 were once-biopsied and 11 were twice-biopsied. The primary endpoints were implantation rate (IR), clinical pregnancy rate (CPR), live birth rate (LBR), and miscarriage rate (MR). Embryo transfers involving embryos biopsied between May 2022 and March 2024 were included. Participants/materials, setting, methods Once-frozen embryos were cultured to Day 5 or 6, biopsied, frozen, and later thawed for transfer. Once-biopsied TBR embryos were frozen (without prior biopsy), then thawed, biopsied, refrozen, and thawed again for transfer. Twice-biopsied TBR embryos were biopsied, frozen, thawed, biopsied again, refrozen, and thawed for transfer. Main results and the role of chance There were no significant differences in clinical outcomes between once-frozen and TBR embryos: IR (64% vs 66%), CPR (56% vs 52%), and LBR (50% vs 52%). Among TBR embryos, once-biopsied and twice-biopsied showed no significant differences in IR (67% vs 64%), CPR (57% vs 36%), LBR (57% vs 36%), or MR (5.7% vs 27%). This suggested that a second vitrification cycle and a repeated biopsy did not negatively impact pregnancy outcomes. Limitations, reasons for caution With 47 TBR embryos, this study represents one of the largest investigations of TBR embryos to date. However, 11 twice-biopsied embryos was likely an insufficient sample to detect statistical differences between once- and twice-biopsied TBR embryos. Given the absolute differences in clinical outcomes, large studies and meta-analyses would be valuable. Wider implications of the findings This study has key implications for cases where the initial biopsy yields inconclusive genetic results, occurring in around 2% of PGT-A cases at this centre. As patients with poorer prognoses often have fewer retrieved eggs, TBR embryos could increase the number available for transfer, potentially improving clinical outcomes. Trial registration number No