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The Correlation of Inner Cell Mass Grade and Trophectoderm Grade on Patient Clinical Outcomes Following an Embryo Transfer


To analyze the relationship between embryo morphology grades and the significance on patient pregnancy rates following a single euploid frozen embryo transfer (FET).


Retrospective study.

Materials and Methods:

This study included 694 FET cycles of single euploid embryos performed in 2023.  Embryos were graded based on the morphology of the inner cell mass (ICM) and trophectoderm cells, at the time of vitrification using the SART grading scale. Transfers were separated into 4 groups based on the embryo grade: Good/Good (n=266), Good/Fair (n=159), Fair/Good (n=95), and Fair/Fair (n=174). Embryo survival, pregnancy and implantation rates were analyzed and compared for each group. Transfers with untested patient embryos, multiple embryos or donor eggs were excluded from the study. Statistical analyses were performed using an N-1 Chi-squared test.


No differences in patient ages or embryo survival rates were noted for any of the embryo grade groups. Embryos graded Fair/Fair showed significantly lower positive β-HCG, clinical, ongoing, and implantation rates compared to embryos that were graded Good/Good or Good/Fair (Table 1).

Table 1. Pregnancy outcomes for different grades of embryos

Embryo Grade
Good/Good Good/Fair Fair/Good Fair/Fair
n 266 159 95 174
Patient age (mean ± SD) 34.9 ± 4.0 35.5 ± 3.6 35.4 ± 4.1 35.3 ± 4.3
Embryos warmed 268 160 98 174
Embryos survived (%) 266 (99.3%) 159 (99.4%) 95 (96.9%) 174 (100%)
Embryos transferred 266 159 95 174
Positive β-HCG rate (%) 66.5a 65.4b 61.0 54.6a,b
Clinical pregnancy (%) 63.9c 62.3d 54.7 50.0c,d
Ongoing pregnancy (%) 58.6e 60.4f 51.6 45.4e,f
Gestational Sacs 171 100 52 87
Implantation rate (%) 64.7g 62.9h 54.7 50.0g,h

Values with the same superscript are significantly different. ap=0.012, bp=0.045, cp=0.003, dp=0.024, ep=0.006, fp=0.006, 8p=0.002, hp=0.018


Embryos graded as Good/Good showed the highest clinical outcomes compared to the other embryo groups. While it has been suggested that embryo grade does not affect the overall clinical outcome as long as the embryo is euploid, this data suggests grade still plays a role. Embryos graded as Good/Good and Good/Fair showed a significant increase in positive β-HCG, clinical pregnancy, ongoing pregnancy, and implantation rates. 





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