P-207 Are the time of expansion and morphology of the blastocyst after thawing, assessed by time-lapse technology, decisive for implantation?

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Abstract Study question Can blastocyst first expansion time after thawing, complete expansion, and morphology evaluated by time-lapse technology predict implantation? Summary answer Lower blastocyst expansion time after thawing and higher blastocyst quality assessed at the time of transfer are associated with a higher probability of clinical pregnancy What is known already Conflicting results have been published concerning the time of first and complete re-expansion of blastocyst after thawing or its quality and the attainment of pregnancy. Some studies reported no differences in pregnancy rate (PR) with different re-expansion duration, whereas other retrospective studies identified the degree of re-expansion, assessed within 6 hours after thawing, as the best predictor. Similarly, both studies reporting associations and non-associations between blastocyst morphology and PR have been published. Study design, size, duration We prospectively evaluated the time of first and complete expansion and quality grade of 141 homologous single blastocysts after thawing and relate the results to PR. The enrolled patients had a mean age of 38.7 ± 5.4 years. Morphokinetic parameters were evaluated using the Embryoscope time-lapse system. The study is currently ongoing. Participants/materials, setting, methods The study was conducted on 141 patients iundergoing homologous PMA cicles. Time lapse Embryoscope was used to assess post-thawing morphokinetic parameters as possible early markers of successful implantation. Time to first trophectoderm expansion, time and morphology two hours after thawing, and time and morphology of the blastocyst at the time of transfer were evaluated and recorded. Statistical analysis was performed using SPSS statistical package 28.0. Main results and the role of chance Both time of first (TfE) and maximum (TmE) blastocyst expansion were associated with a higher probability of pregnancy. Median TfE in women achieving pregnancy was 0.97 hours (range: 0.29-2.2) vs 1,4 (range 0.2-3.3) in those not achieving pregnancy (p < 0.001). Similarly, TmE was lower in pregnant women (p < 0.05). When blastocyst expansion occurred within 2 h, a PR of 71% was obtained vs 16% in women where expansion was post-poned (p < 0.001). ROC analysis showed that a TfE of 1,19h predicted attainment of pregnancy with an accuracy of 75%, a sensitivity of 75% and a specificity of 70% (p < 0.001). Blastocyst quality was found as another independent predictor of attainment of pregnancy. PR resulted of 21, 31,5 and 63,3% respectively with 0, 1 and 2 grade of blastocyst quality (p < 0.001, OR = 7.7). Limitations, reasons for caution Our study is preliminary and to draw firm conclusions, a higher number of blastocysts should be evaluated. The study is ongoing. Statistical correction for partners semen quality should be also performed. Wider implications of the findings Our preliminary results showed that TfE, TmE after thawing, and blastocyst quality are predictors of pregnancy achievement. Our study suggests that time lapse technology is useful for predicting pregnancy with good accuracy when transfer is performed after blastocyst freezing. Trial registration number not applicable

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