BLASTOCYST SIZE AS A PREDICTOR OF PREGNANCY: A MULTICENTER META-ANALYSIS

Background and Aims

The Gardner criteria, widely used to evaluate blastocyst morphology, is a significant predictor of clinical pregnancy. However, the roles of factors like embryo size and inner cell mass (ICM) ratio remain unclear. Studies suggest that ICM, trophectoderm (TE), and zona pellucida (ZP) areas may influence pregnancy outcomes, but findings are inconsistent. This study investigates the relationship between these morphological features and pregnancy success through a meta-analysis.

Methods

Between June 2011 and May 2022, 1,392 single static images of day-5 fresh embryos were collected from four IVF clinics, comprising two in Korea and two in the USA. Hatching or hatched stage embryos were excluded due to their differing measurement requirements. ICM, TE, and ZP boundaries were manually annotated by five embryologists with over 10 years of experience and the areas of the ICM, inner TE, and inner ZP were compared using the bounding boxes calculated for each segment. The study involved regression analyses at each clinic to identify significant morphological features influencing pregnancy outcomes. Meta-analyses were then conducted on characteristics with inter-clinic differences.

Results

TE bounding box area was significant in three of four clinics. Meta-analysis confirmed statistical significance for TE bounding box width (estimator: 0.0192, confidence interval: [0.009, 0.028]) and height (estimator: 0.0193, confidence interval: [0.010, 0.027]). ZP bounding box area was significant in one clinic but showed no significance in the meta-analysis for width (estimator: 0.006, confidence interval: [-0.005, 0.026]) or height (estimator: 0.0105, CI: [-0.005, 0.027]). ICM area had no significant impact across clinics.

Conclusions

This multicenter meta-analysis identifies the inner trophectoderm area as a significant predictor of pregnancy outcomes, emphasizing its potential role in embryo assessment. The lack of significance for ICM may be due to imaging variability, underscoring the need for standardized evaluation methods.