The predictive value of post-warming morphometric changes parameters for embryo implantation.

OBJECTIVE: To investigate whether post-warming blastocyst morphometric dynamics assessed by time-lapse imaging (TLI) are associated with implantation in intracytoplasmic sperm injection cycles with deferred embryo transfer. METHODS: This observational cohort study included 822 vitrified-warmed high-quality blastocysts with known implantation outcomes, evaluated between January and October 2024 at a private university-affiliated in vitro fertilization centre. Post-warming morphometric parameters were recorded during a 4-hour incubation period, including initial blastocyst area, maximum blastocyst area (MXBA), initial zona pellucida thickness, minimum zona pellucida thickness (MZP), and blastocyst re-expansion. Associations with implantation were assessed using multivariable logistic regression. A composite weighted score incorporating MXBA, MZP, and blastocyst re-expansion was developed from the regression coefficients and analysed as a continuous variable. Restricted cubic spline modelling was used to assess potential non-linear associations. RESULTS: MXBA (OR=1.078; 95% CI 1.029-1.198; p=0.048), MZP (OR=0.923; 95% CI 0.856-0.995; p=0.038), and blastocyst re-expansion (OR=1.183; 95% CI 1.010-1.386; p=0.036) were independently associated with implantation. Each one-standard-deviation increase in the composite weighted score was associated with a 21.6% increase in the odds of implantation (OR=1.216; 95% CI 1.055-1.403; p=0.007). Spline analysis showed a progressive increase in implantation probability across the score range, without strong evidence of non-linearity. CONCLUSION: Quantitative post-warming morphometric assessment provides clinically relevant information on blastocyst implantation potential. A composite score integrating MXBA, MZP, and blastocyst re-expansion may support embryo selection in frozen-thawed embryo transfer cycles.