P-176 Impact of inner cell mass position on embryo implantation potential: control strategies

Abstract Study question Is embryo implantation affected by the position of the inner cell mass (ICM) at the moment of the biopsy? Summary answer Assisted hatching (AH) at polar body (PB) localisation increases the likelihood of inner location of the ICM; this is correlated with higher pregnancy rates. What is known already Preimplantation genetic testing for aneuploidies (PGT-A) helps reduce the risk of implantation failure and miscarriage. Trophectoderm biopsy is performed to analyse the embryo’s genetic content prior to transfer. The integrity and health of the ICM during this procedure is crucial for the potential development of the embryo. The position and condition of the ICM can significantly influence implantation and pregnancy rates. Studies suggest that damage or alterations to the ICM during biopsy may negatively impact success rates. Therefore, more studies on the positioning of the ICM during trophectoderm biopsy at blastocyst stage are vital. Study design, size, duration A retrospective study analysing 174 videos of embryos undergoing trophectoderm biopsy for PGT-A. Inner cell mass position within the blastocyst, prior to trophectoderm biopsy, was noted from the last video capture. ICM position was classified as: inside the zona pellucida (ZP) (In); outside the ZP (Out), o located within the hatched zone (Mid). The pregnancy rate, clinical pregnancy rate, and miscarriage rate were evaluated. Participants/materials, setting, methods Embryos were cultured in global total medium(Life Global) and incubated in time-lapse incubators(Geri,Genea-BIomedix) for 5/6 days. The AH was performed on day+3 of cleavage using Octax laser. The position of ICM with respect to the 1st PB was performed in a previous study on 150 embryos. Localisation categories were: coincidence; adjacent; non-adjacent or opposite. For group comparisons, chi-square test with Yates correction was used. Differences were considered statistically significant when p < 0.05. Main results and the role of chance At the time of trophectoderm biopsy, 112 blastocysts had the ICM within the zona pellucida(ZP), 33 externally, and 30 in an intermediate position. The pregnancy rates for internal(In), middle(Mid) and external(Out) position of the ICM were 63.4%, 50% and 30.3% respectively. Significant differences were observed among groups(p = 0.003). Similarly, clinical pregnancy rates showed statistical differences(p = 0.002), with rates of 57.9% for In, 36.7% for Mid, and 27.3% for Out ICM localisation. No significant differences were found among the different positions regarding miscarriage rates(p = 0.63). These findings suggest that embryos with an internal ICM position have higher success rates, while an external ICM location is associated to lower rates. Using the first polar body(PB) position as reference point to where to do the assisted hatching(AH) hole, we found that 72.7% of embryos had the ICM located opposite and/or non-adjacent to the PB, while 18.7% were adjacent or coincided. An additional 8.67% could not be determined due to embryo movement during time-lapse video recording. The emergence of the ICM at the same or adjacent sites as the AH hole was associated with premature exit of the exterior ICM or its protrusion, both of which adversely affected pregnancy and clinical pregnancy rates. Limitations, reasons for caution The number of embryos analysed in this study limits the interpretation and extension of the results obtained. Therefore, an increase in the number of embryos studied may consolidate these preliminary results. Wider implications of the findings These findings suggest that inner cell mass positioning during biopsy is critical for optimising clinical outcomes associated with IVF-treatments, specifically through assisted hatching strategies. Performing the AH hole at the location of the first PB increases the probability that the ICM remains protected within the zona pellucida during embryo biopsy. Trial registration number No