P-199 Multiple Freeze-Thaw Cycles Are Associated with Poorer Embryo Morphology and Live Birth Rates in PGT-Tested FET

Abstract

Study question How do frozen embryo transfer (FET) outcomes of preimplantation genetic testing (PGT)-tested embryos compare between those undergoing two versus a single freeze-thaw cycle(s)? Summary answer PGT-tested embryos subjected to two freeze-thaw cycles were noted to have poorer morphology, higher miscarriage rates, and lower live birth rates. What is known already For various clinical reasons, patients who initially froze untested embryos after controlled ovarian hyperstimulation may later thaw those embryos for PGT. However, the impact of two freeze-thaw cycles on embryo potential and FET outcomes remains unclear. Limited research exists on how repeated freeze-thaw cycles affects embryo quality, making patient counseling challenging. This study aims to clarify the effects of two freeze-thaw cycles on FET outcomes. Study design, size, duration A retrospective chart review analyzed FET cases with PGT-tested embryos at Weill Cornell Center for Reproductive Medicine (2020–2024). Among 4724 FETs, 4542 involved testing fresh embryos (T1), while 182 involved thawing frozen embryos for PGT, refreezing, and thawing again for FET (T2). Participants/materials, setting, methods Individuals aged 18–45 who underwent natural cycle or programmed FET with a PGT-tested embryo at a New York academic multicenter clinic were included. Reasons for embryo thawing for PGT were recorded. Blastocysts were categorized by final thaw morphology: excellent (≥3AA), good (3-6AB, 3-6BA, 1-2AA), average (3-6BB, 3-6AC, 3-6CA, 1-2AB, 1-2BA), and poor (1-6BC, 1-6CB, 1-6CC, 1-2BB). Descriptive statistics assessed population characteristics, and Fisher’s exact test compared FET outcomes between T1 and T2. Main results and the role of chance Between 2020 and 2024, 4542 FETs used PGT-tested embryos thawed once (T1). Additionally, 254 embryos underwent thawing for PGT, leading to 182 FETs (T2) of 183 euploid embryos among 127 individuals. Of 72 individuals who did not proceed with FET after thawing, 47 had no euploid embryos. The reasons for embryo thawing for PGT included prior pregnancy loss or failed implantation after untested transfers (n = 55), age-related aneuploidy screening or grouping from multiple retrieval cycles for PGT-A (n = 33), sex selection (n = 19), PGT-M (n = 13), prior termination for aneuploidy (n = 7), and rebiopsy (n = 2). Embryo morphology was poorer after a second thaw, with fewer “excellent” (T2: 0.5% vs. T1: 4.4%, p=.007) and “good” embryos (T2: 19.8% vs. 22.2%, p=.007). Live birth rates were lower in T2 (39.6% vs. 54.6%, p<.001), as were implantation rates per transfer (52.2% vs. 61.0%, p=.020) and per embryo (51.9% vs. 59.9%, p=.032). Miscarriage rates were higher (18.9% vs. 9.4%, p=.004). Within T2, individuals with a history of one or more pregnancy losses or failed implantation had comparable live birth and miscarriage rates to those with other reasons for undergoing a freeze-thaw cycle. Limitations, reasons for caution This single-center, retrospective study has limited generalizability and excludes rare cases of embryos not surviving the second thaw, necessitating larger multicenter studies for validation. Wider implications of the findings Multiple freeze-thaw cycles pose potential risks, including higher miscarriage rates and lower live birth rates. These findings emphasize the need for individualized counseling and treatment plans based on risk-benefit profiles. These findings also support the need for further investigation into laboratory freeze-thaw protocols to optimize embryo potential and outcomes. Trial registration number No