LAUSR

To investigate the applicability and safety of the blastocyst grading system for borderline blastocysts assessed by measurement of the inner cell mass (ICM) and trophectoderm (TE) parameters. A total of 361 borderline blastocysts were classified as B-B-, B-C, and CB/CB-blastocysts based on the parameters of the ICM and TE in frozen-thawed embryo transfer cycles, and these embryos were divided into groups A, B, and C. The primary outcome measures were clinical pregnancy rate (CPR), live birth rate (LBR), gestational age (GA) at birth, birth weight, and malformation rate. Four embryologists independently evaluated 90 embryos, with inter- and intra-observer agreement analyzed using Fleiss’ kappa coefficient. The CPR (9.1%) and LBR (5.5%) in group C were lower than those in groups A (34.9% and 25.6%, respectively) and B (25.3% and 19.0%, respectively). There were no differences in GA at birth, birth weight, or malformation rate among groups A, B, and C. Binary regression analysis revealed that embryos with an ICM grade of C (OR 0.158; 95% CI 0.073–0.439; P < 0.001) had a lower likelihood of LBR than those with an ICM grade of B−. The inter- and intra-observer agreement between embryologists in terms of embryo morphological grading and clinical decision-making ranged from good (K > 0.61) to very good (K > 0.81). The modified grading system to assess borderline blastocysts is safe and effective and improves the consistency of embryo assessment.