PURPOSE & OBJECTIVES
We aim to establish optimal embryo grade criteria for predicting clinical pregnancy and verify if the criteria differ based on age.
MATERIAL & METHODS
We conducted a retrospective study on 2,605 Day 5 blastocyst images collected from seven IVF clinics between June 2011 and May 2022. The blastocyst stages, ICM, and TE grades were manually labeled and assessed by five experienced embryologists according to the Gardner grading criteria. We divided the dataset into two groups based on age (<37 and ≥37) and performed a logistic regression analysis with stage, ICM, and TE as independent variables and clinical pregnancy (presence of a gestational sac) as the dependent variable.
In the group under 37 years old, the probability of pregnancy increased when the embryo stage was 4 or higher compared to stage 3 (p < 0.05), but there was no significant difference between stages 4, 5, and 6. For ICM and TE, the probability of pregnancy significantly increased in the order of grade C < B < A (p < 0.05). In the group aged 37 and older, the probability of pregnancy increased in the order of stage 3 < 4 < 5 (p < 0.05), with no significant difference between stages 5 and 6. For ICM and TE grades, the probability of pregnancy increased when the grade was B rather than C (p < 0.05), but there was no significant difference between grades B and A.
The Gardner grading system is widely used for evaluating embryo quality, but the criteria for defining a high-quality embryo are ambiguous. We demonstrated that for the under-37 group, the cut-off for high-quality embryos with an increased likelihood of pregnancy was 4AA and above, and for the over-37 group, it was 5BB and above. Further studies are warranted to confirm our findings and investigate the underlying mechanisms that explain the age-dependent differences in blastocyst grading.
Our study highlights the importance of age-specific criteria in defining a good-quality blastocyst for successful clinical pregnancy. Specifically, the advanced blastocyst stage was more of an important predictor of clinical pregnancy than ICM or TE grades in the older group.