Morphometric assessment of blastocysts: relationship with the ongoing pregnancy rate

Abstract

Objective: To explore a morphometric grading system for blastocysts that is associated with ongoing pregnancy. Design: Cross-sectional study. Setting: None. Patients(s): All consecutive vitrified blastocysts at our center from July 2018 to November 2021 that were transferred in single blastocyst transfer cycles until January 2022. Intervention(s): None. Main Outcome Measure(s): The ongoing pregnancy rate after a single vitrified-warmed blastocyst transfer. Interobserver agreement on morphometric values among embryologists. Result(s): Three morphometric variables (blastocyst diameter, area of inner cell mass [ICM], and the estimated trophectoderm cell count) were used to evaluate the expansion, ICM, and trophectoderm morphology. During the study period, 585 blastocysts were involved in this study. Of the 3 morphometric variables, ICM area (per 500 μm2, adjusted odds ratio, 1.19; 95% confidence interval, 1.09−1.30) and estimated trophectoderm cell count (per 10 cells, adjusted odds ratio, 1.25; 95% confidence interval, 1.12−1.39) were significantly associated with the ongoing pregnancy rate after adjustment for confounding factors. The ongoing pregnancy rate was 2.0% (1/49) with an ICM area of 3,500 μm2 and >110, respectively. Interobserver agreement on the blastocyst diameter, ICM area, and the estimated trophectoderm cell count was excellent-to-good among 5 embryologists (intraclass correlation coefficients: 0.99, 0.87, and 0.91, respectively). Conclusion(s): Morphometric values of ICM and trophectoderm are promising predictors of pregnancy success. The high reproducibility suggests that the morphometric variables will contribute to identifying blastocysts with the highest developmental potential as well as those that will not result in a successful pregnancy.

Keywords

• Blastocyst morphology
• morphometry
• ongoing pregnancy rate
• inner cell mass
• trophectoderm